[SOLVED] Rearrange to solve

Okay I feel dumb asking this, I should know this, but it's been so long since I've bothered to use any algebra I've completely forgotten how it would be done.

Consider this equation.

a = b / (b + c)

Pretend we have a value for a and c, how would you rearrange this to find b? It being on both the top and bottom of the division is what's confusing me.

I did this but I know it's completely wrong:

a * c = b /b

but that would mean

a * c = 1

!!!

Can somebody point out what I'm doing wrong?

Cheers