10(1 + 3b) = -20
Isolate b.
Apply the distributive property: a(b + c) = ab + ac.
10 + 30b = -20
Subtract 10 from both sides.
10 + 30b - 10 = -20 - 10
30b = -30
Divide both sides by the coefficient, 30.
b = -1
-1
