-21=8b-b

Solution for -21=8b-b equation:

Simplifying
-21 = 8b + -1b

Combine like terms: 8b + -1b = 7b
-21 = 7b

Solving
-21 = 7b

Solving for variable 'b'.

Move all terms containing b to the left, all other terms to the right.

Add '-7b' to each side of the equation.
-21 + -7b = 7b + -7b

Combine like terms: 7b + -7b = 0
-21 + -7b = 0

Add '21' to each side of the equation.
-21 + 21 + -7b = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -7b = 0 + 21
-7b = 0 + 21

Combine like terms: 0 + 21 = 21
-7b = 21

Divide each side by '-7'.
b = -3

Simplifying
b = -3