Answer:
a. 4 yards (4-0)
b. 6 yards (10-4)
c. 7 yards (17-10)
The marginal product is the change in your output as a result of one unit increase in your input.
d. The marginal product of labor potentially increases from one to three workers due to the fact that whenever you increase the input form one side, it results in the the more output from the other side. As the number of workers would increase, so does the productivity and so does the marginal productivity of each worker.
Hope this helps.
Good luck buddy.