Since you want to solve for one variable in your equation, and since there are two in it altogether, you will end up with the other in your answer, always. I'll show you how to figure out this one.
Let us solve for x.
First step: Add 5b to both sides.
-5b + 5x + 5b = 12b + 5b
5x = 17b
Second step: Divide both sides by 5.
5x/5 = 17b/5
x = 17/5b
Final answer -
x = 17/5b
(Note that the /s are the fraction bars)
Hope this helps! :D
And if you have anymore questions like this that you need help on, let me know!