18. A farmer is trying to determine how much fencing to buy
to make a square holding pen with a 6-foot gap for a gate.
The length of fencing, f, in feet, required as a function of
area, A, in square feet, is given by f(A) = 4√A - 6. Evaluate
the function from 20 ft2 to 100 ft2 by calculating points
every 20 ft².