Suppose Charles owns a​ lawn-mowing company. Assume that without​ workers, no yards are mowed. When he hires one​ worker, he is able to mow 4 yards per day. With two​ workers, he can mow 10 yards per​ day, and with three​ workers, he can mow 17 yards per day.

a. The marginal product of the first worker is ___________ yards per day.
b. The marginal product of the second worker is ___________ yards per day.
c. ​Last, the marginal product of the third worker is ___________ yards per day.
d. The marginal product of labor potentially increases​ (from one to three​ workers) due to ________