"Instruction references undefined symbol at 0x00400028" when running the code

Question

.data
prompt_input: .asciiz "Enter value for "
prompt_output: .asciiz "Result: "
newline: .asciiz "\n"

.equation1: .asciiz "(A NAND B) NOR C"
.equation2: .asciiz "(A XOR B) AND C"
.equation3: .asciiz "(A * B) DIV C"
.equation4: .asciiz "(A MOD B) + C"

.text
.globl main

main:
    # Display menu to the user
    li $v0,4
    la $a0,equation_menu
    syscall
    
    # Prompt user for equation choice
    li $v0,5
    syscall
    move $t0,$v0 # Store user's choice
    
    # Depending on user's choice, execute corresponding equation
    beq $t0,1,equation1
    beq $t0,2,equation2
    beq $t0,3,equation3
    beq $t0,4,equation4
    
    # Invalid choice, exit
    li $v0,10
    syscall
    
equation1:
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t1,$v0 # Store A
    
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t2,$v0 # Store B
    
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t3,$v0 # Store C
    
    # Calculate (A NAND B) NOR C
    nor $t4,$t1,$t2 # NAND operation
    nor $t5,$t4,$t3 # NOR operation
    
    # Display result
    li $v0,4
    la $a0,prompt_output
    syscall
    move $a0,$t5
    li $v0,1
    syscall
    j exit
    
equation2:
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t4,$v0 # Store A
    
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t5,$v0 # Store B
    
    li $v0,4
    la $a0,prompt_input
    syscall
    li $v0,5
    syscall
    move $t6,$v0 # Store C
    
    # Calculate (A XOR B) AND C
    xor $t7,$t4,$t5 # XOR operation
    and $s0,$t7,$t6 # AND operation
    
    # Display result
    li $v0,4
    la $a0,prompt_output
    syscall
    move $a0,$s0
    li $v0,1
    syscall
    j exit
    
equation3:
    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t1, $v0 # Store A
    
    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t2, $v0 # Store B
    
    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t3, $v0 # Store C
    
    # Calculate (A * B) / C
    mul $t4, $t1, $t2 # Multiplication operation
    div $t5, $t4, $t3 # Division operation
    
    # Display result
    li $v0, 4
    la $a0, prompt_output
    syscall
    move $a0, $t5
    li $v0, 1
    syscall
    j exit
    
equation4:
    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t1, $v0 # Store A
    
    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t2, $v0 # Store B

    li $v0, 4
    la $a0, prompt_input
    syscall
    li $v0, 5
    syscall
    move $t3, $v0 # Store C
    
    # Calculate (A MOD B) + C
    div $t4, $t1, $t2 # Modulo operation
    mfhi $t5
    add $t5, $t5, $t3 # Addition operation
    
    # Display result
    li $v0, 4
    la $a0, prompt_output
    syscall
    move $a0, $t5
    li $v0, 1
    syscall
    j exit
    
exit:
    # Exit program
    li $v0,10
    syscall

when i run this program, it displays the error "Instruction references undefined symbol at 0x00400028" and this "0x00400028] 0x3c010000 lui $1, 0 [equation_menu] ; 6: la $a0,equation_menu"

I tried many ways like changing asciiz into asciz, adding main and deleting spaces but nothing works.