EXPLANATION
Applying the sum of interior angles theorem give us the following relationship:
60 + 3x + (x+20) = 180
Removing the parentheses:
60 + 3x + x + 20 = 180
Adding like terms:
80 + 4x = 180
Subtracting -80 to both sides:
4x = 180 - 80
Subtracting numbers:
4x = 100
Dividing both sides by 4:
x = 100/4
Simplifying:
x = 25
Then, the missing angles are:
25 + 20 = 45 degrees
3*25 = 75 degrees
