Akarie, this is the solution to the problem:
Let's recall that:
Supplementary angles are those that add up to 180 degrees, and in other hand, Complementary angles are those that add up to 90 degrees.
Upon saying that,
the angles in the picture are complementary because they add up to 90 degrees.
Akarie, to solve for x, this is the procedure:
x + (x - 30) = 90 (Complementary angles)
x + x - 30 = 90
Adding 30 at both sides of the equation:
x + x - 30 + 30 = 90 + 30
2x = 120
Dividing by 2 at both sides of the equation:
2x/2 = 120/2
x = 60 (This means we have two angles: the greater measures 60 degrees and the smaller measures 30 degrees)