#### Answer

b=7

#### Work Step by Step

We fist combine like terms to obtain that $13=3b-8$. We need to get the b alone, so we cancel out the subtraction by adding 8 on both sides. This leaves us with the equation 3b=21. We use division to cancel out multiplication, so we divide both sides by 3 to get that b=7. We plug 7 in for b and confirm that our answer is, indeed, correct.