Ok, so
Let me draw the situation here below:
So, we want to find the value of x.
For this, we have to remember that the sum of the internal angles of any triangle will always be 180°.
And we got the following angles:
A = 2x+20
B = 7x+7
C = 90
And we know that:
2x + 20 + 7x + 7 + 90 = 180°
9x + 117 = 180
We let numbers in one side of the equation and "x terms" in the other side. Like this:
9x = 63
Therefore, the value of x is 7.