42=-2(21-m)+4(m-3)

Solution for 42=-2(21-m)+4(m-3) equation:

Simplifying
42 = -2(21 + -1m) + 4(m + -3)
42 = (21 * -2 + -1m * -2) + 4(m + -3)
42 = (-42 + 2m) + 4(m + -3)

Reorder the terms:
42 = -42 + 2m + 4(-3 + m)
42 = -42 + 2m + (-3 * 4 + m * 4)
42 = -42 + 2m + (-12 + 4m)

Reorder the terms:
42 = -42 + -12 + 2m + 4m

Combine like terms: -42 + -12 = -54
42 = -54 + 2m + 4m

Combine like terms: 2m + 4m = 6m
42 = -54 + 6m

Solving
42 = -54 + 6m

Solving for variable 'm'.

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

Add '-6m' to each side of the equation.
42 + -6m = -54 + 6m + -6m

Combine like terms: 6m + -6m = 0
42 + -6m = -54 + 0
42 + -6m = -54

Add '-42' to each side of the equation.
42 + -42 + -6m = -54 + -42

Combine like terms: 42 + -42 = 0
0 + -6m = -54 + -42
-6m = -54 + -42

Combine like terms: -54 + -42 = -96
-6m = -96

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

Simplifying
m = 16