Geometry Question. . . Please Help! :)

Angle A & Angle B are complementary (total measurement of 90 degrees)
Find Angle A & Angle B

The measurement for Angle A= 8x-7
The measurement for Angle B= x-11

Can you please explain to me how you do this.

A = 8x - 7
B = x - 11

A + B = 90
8x - 7 + x - 11 = 90
9x - 18 = 90
9x = 108
x = 12

A = 8x - 7 = 8 * 12 - 7 = 96 - 7 = 89
B = x - 11 = 12 - 11 = 1

Wow, the 1st answerer really know his stuff. Pretty damn smart.