21=-7b

Solution for 21=-7b equation:

Simplifying
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