b. The sensitivity analysis will give a range on the objective function coefficients for full-time drivers hired at each time. The range with the lowest upper bound indicates the rate at which the solution will change.

c. The dual variable on the part-time availability constraint gives the marginal benefit for one driver. Multiply this by 10 to get an upper bound on the marginal benefit for 10 drivers. If this number is less than 100 the add is not justified. If it is more than 100 the range analysis should be consulted to see if the range of the right side is more than 10 from the current value.