42=3+a

Solution for 42=3+a equation:

Simplifying
42 = 3 + a

Solving
42 = 3 + 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.
42 + -1a = 3 + a + -1a

Combine like terms: a + -1a = 0
42 + -1a = 3 + 0
42 + -1a = 3

Add '-42' to each side of the equation.
42 + -42 + -1a = 3 + -42

Combine like terms: 42 + -42 = 0
0 + -1a = 3 + -42
-1a = 3 + -42

Combine like terms: 3 + -42 = -39
-1a = -39

Divide each side by '-1'.
a = 39

Simplifying
a = 39