Answer:
D: 20 degrees
Explanation:
First, we add 3x+10 and x together because they are within a right angle, which is 90 degrees. This gives the equation 4x+10=90. We solve from here.
We subtract 10 from both sides to isolate the x-variable. 90 minus 10 equals 80. This gives us the equation 4x=80. To further isolate the x-variable, we divide both sides by 4. 80 divided by 4 equals 20.
This leaves us with x=20.
Hope this helped!