-78-12=15a

Solution for -78-12=15a equation:

Simplifying
-78 + -12 = 15a

Combine like terms: -78 + -12 = -90
-90 = 15a

Solving
-90 = 15a

Solving for variable 'a'.

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

Add '-15a' to each side of the equation.
-90 + -15a = 15a + -15a

Combine like terms: 15a + -15a = 0
-90 + -15a = 0

Add '90' to each side of the equation.
-90 + 90 + -15a = 0 + 90

Combine like terms: -90 + 90 = 0
0 + -15a = 0 + 90
-15a = 0 + 90

Combine like terms: 0 + 90 = 90
-15a = 90

Divide each side by '-15'.
a = -6

Simplifying
a = -6