Geomtrey question :/ Helppp!(below)

In Triangle DEF...m Find the measure of angle F.

I tried this but I got a negative answer. So can someone please help me!?

Thanks in Advance :)

Sum of the angles of a triangle = 180°
=> 4x - 10 + 8x - 5 + x^2 + 2x + 10 = 180
=> x^2 + 14x - 185 = 0
=> x = (1/2) [- 14 ± √(196 + 740)]
=> x = (1/2) [- 14 + 30.6] ... [discarding the negative value of x which is not feasible]
=> x = 8.3
=> m∠F = x^2 + 2x + 10 = 95.5°.

Sum of the interior angles of a triangle is 180 degree

so

4x - 10 + 8x - 5 + x² + 2x + 10 = 180

x² + 14x - 185 = 0
solve it by using quadratic formula
x = 8.3

Substitute it
angle F is about 95.5 degree

I came up with 95.5 deg.

Add the 3 angles, set the total equal to 180 deg. and use the quadratic equation to solve the resulting equation.