21=-3(23-b)+3(b-2)

Solution for 21=-3(23-b)+3(b-2) equation:

Simplifying
21 = -3(23 + -1b) + 3(b + -2)
21 = (23 * -3 + -1b * -3) + 3(b + -2)
21 = (-69 + 3b) + 3(b + -2)

Reorder the terms:
21 = -69 + 3b + 3(-2 + b)
21 = -69 + 3b + (-2 * 3 + b * 3)
21 = -69 + 3b + (-6 + 3b)

Reorder the terms:
21 = -69 + -6 + 3b + 3b

Combine like terms: -69 + -6 = -75
21 = -75 + 3b + 3b

Combine like terms: 3b + 3b = 6b
21 = -75 + 6b

Solving
21 = -75 + 6b

Solving for variable 'b'.

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

Add '-6b' to each side of the equation.
21 + -6b = -75 + 6b + -6b

Combine like terms: 6b + -6b = 0
21 + -6b = -75 + 0
21 + -6b = -75

Add '-21' to each side of the equation.
21 + -21 + -6b = -75 + -21

Combine like terms: 21 + -21 = 0
0 + -6b = -75 + -21
-6b = -75 + -21

Combine like terms: -75 + -21 = -96
-6b = -96

Divide each side by '-6'.
b = 16

Simplifying
b = 16