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

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

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

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

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

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

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

Solving
42 = -54 + 6y

Solving for variable 'y'.

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

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

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

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

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

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

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

Simplifying
y = 16