Chapter 2 - Solving Equations - 2-7 Solving Proportions - Practice and Problem-Solving Exercises - Page 127: 31

$b=-20/3$

Recall, cross multiplying refers to when we multiply the numerator of the first fraction by the denominator of the second fraction and set that equal to the numerator of the second fraction times the denominator of the first fraction. We first cross multiply to get that $ 3b-12=6b+8$. We then subtract by 3b on both sides to get that $-12=3b+8$. Then, we subtract 8 on both sides to get that $-20=3b$. We finally divide by 3 on both sides to get that $b=-20/3$.