Algebra 1: Common Core (15th Edition)

$b=7$
Because 5 and -13 are like terms, we can add them to simplify the equation to $13=3b-8.$ We now need to get the b alone. Thus, we cancel out the subtraction by adding 8 on both sides. This leaves us with the equation $3b=21.$ In order to cancel out multiplication, we use division, 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.