Two angles are Supplementary, when they add up to 180 degrees. Hence:
Let x and y be both angles (x is the angle we are looking for);
x + y = 180° (1)
x = 1/5y (2)
We need to solve the system of equations, as follows:
Replacing equation 2 on equation 1:
1/5y + y = 180
y = 150°
Replacing the value of y in equation 2:
x = 1/5(150)
x = 30°
ANSWER
The measurement of the angle is 30°