Answer:
Third option.
Step-by-step explanation:
You need to remember that the formula used to calculate the arc lenght is:

Where "r" is the radius and "C" is the central angle in radians.
You need to solve for "C":
You know the radius and the arc lenght, therefore, you can substitute values to calculate the central angle in radians. Therefore, this is:

(f+g-k)(x) means to add the equations f(x) and g(x) then subtract k(x)
2x^2 + 3x + 4x - 9 = 2x^2 +7x -9
2x^2 + 7x - 9 - x^2 -7x = x^2 -9
The answer is : x^2 - 9
-5m-20-80+50m=0
45m=100
m= 20/9