Expressing a constant in function of other prefixed constants - TI-Nspire CAS

Question

I'm trying to do the following operation with my TI-Nspire CAS; I have:

x=a+b

y=a-c

I'd like to get:

y=x-b-c

Thank you so much for your time.

Answer 1

Something like this:

i1:=solve(x=a+b,a)
y:=a-c|i1