The table shows values of a force function f(x), where is measured in meters and f(x) in newtons. Use the Midpoint Rule to estimate the work done by the force in moving an object from x = 4 to x = 20.
x 4 6 8 10 12 14 16 18 20
f(x) 5 5.8 7 8.8 9.6 8.2 6.7 5.2 4.1