84=42+a

Solution for 84=42+a equation:

Simplifying
84 = 42 + a

Solving
84 = 42 + a

Solving for variable 'a'.

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

Add '-1a' to each side of the equation.
84 + -1a = 42 + a + -1a

Combine like terms: a + -1a = 0
84 + -1a = 42 + 0
84 + -1a = 42

Add '-84' to each side of the equation.
84 + -84 + -1a = 42 + -84

Combine like terms: 84 + -84 = 0
0 + -1a = 42 + -84
-1a = 42 + -84

Combine like terms: 42 + -84 = -42
-1a = -42

Divide each side by '-1'.
a = 42

Simplifying
a = 42