12+21=y-42

Solution for 12+21=y-42 equation:

Simplifying
12 + 21 = y + -42

Combine like terms: 12 + 21 = 33
33 = y + -42

Reorder the terms:
33 = -42 + y

Solving
33 = -42 + y

Solving for variable 'y'.

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

Add '-1y' to each side of the equation.
33 + -1y = -42 + y + -1y

Combine like terms: y + -1y = 0
33 + -1y = -42 + 0
33 + -1y = -42

Add '-33' to each side of the equation.
33 + -33 + -1y = -42 + -33

Combine like terms: 33 + -33 = 0
0 + -1y = -42 + -33
-1y = -42 + -33

Combine like terms: -42 + -33 = -75
-1y = -75

Divide each side by '-1'.
y = 75

Simplifying
y = 75