Adding Rational Expressions

Can someone explain how to solve this problem?

x + c - a + b
y...........d

Those periods are only to move the d under the a+b

Thanks,
FlamingFox

I think I got the answer:

xd + cyd - y(a+b)
.......yd

Agian '.' is just used to push the yd over

i don't see a problem that needs to be solved. That is just an expression.
Does it equal something?