You are given the following information concerning how a change in sales force effort impacts sales:

a. A 50% cut in sales force effort reduces sales to 48% of its current value.

b. Sales force effort of 0 reduces sales to 15% of its current value.

c. A 50% increase in sales force effort increases sales by 20%.

d. A saturation of sales effort (a 10-fold increase) increases sales by 35%.

Fit an S-shaped curve as described by Equation (8.1) to these data.