One Angle Of A Triangle Is 20 Degrees. The Second Angle's Measurement Is Four Times The Third. What Is The Measure Of The Third Angle?

 Sum of all the three angles
in a triangle = 180 degrees.
First angle = x
Second angle = y
Third angle =z
x + y + z = 180
Where
x = 20
y = 4z
z = z
So putting the value in equation we will get

20 + 4z + z =180
20 +5z = 180
5z = 180-20
5z = 160z = 160/5
z = 32

So third angle is 32