Total angle sum will always equal 360 degrees. Due to vertical angles theorem, we know the angles opposite the polynomials also equal the polynomials. So, we can double both of them (like solving for perimeter) and sum them to 360.
Thus, 360 = 2(2x + 10) + 2(x+ 5)
360 = 2(2x + 10 + x + 5)
360 = 2(3x + 15)
180 = 3x + 15
165 = 3x
x = 55
