Answer:
15
Explanation:
Since the angles are complementary, that means that when the angles are added together, they are equal to 90*. With this information, we can make the equation: x + (3x + 30) = 90
From this we can add like terms and get 4x + 30 = 90
After this, subtract 30 from both sides: 4x = 60
Divide both sides by 4
x = 15
(Ignore the degree sign in my picture, sorry!)