90-a+b=72

Solution for 90-a+b=72 equation:

Simplifying
90 + -1a + b = 72

Solving
90 + -1a + b = 72

Solving for variable 'a'.

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

Add '-90' to each side of the equation.
90 + -1a + -90 + b = 72 + -90

Reorder the terms:
90 + -90 + -1a + b = 72 + -90

Combine like terms: 90 + -90 = 0
0 + -1a + b = 72 + -90
-1a + b = 72 + -90

Combine like terms: 72 + -90 = -18
-1a + b = -18

Add '-1b' to each side of the equation.
-1a + b + -1b = -18 + -1b

Combine like terms: b + -1b = 0
-1a + 0 = -18 + -1b
-1a = -18 + -1b

Divide each side by '-1'.
a = 18 + b

Simplifying
a = 18 + b