It is important to know that the sum of the three angles inside a triangle add up to 180 degrees. So then we get the following by adding up all three provided angle measures:
3x + (2x + 20) + (4x - 20) = 180
Some algebraic manipulation follows:
3x + 2x + 20 + 4x - 20 = 180
9x = 180
x = 180/9 = 20
The value of x is 20 degrees.
