To find x:
Subtract 10 on both sides.
10 + 2x = 90
-10 -10
Divide 2 on both sides.
2x = 80
--- ---
2 2
This would get x alone.
x = 40
Check:
10 + 2(40) = 90
10 + 80 = 90
90 = 90
The value of x is 40. The angle degree of it is 80 when you multiply 2 by 40.
