A shipping company is attempting to determine how its shipping costs for a month depend on the number of units shipped during a month. The number of units shipped and total shipping cost for the last 15 months are given in the file P12_ 63. xlsx. a. Determine a relationship between units shipped and monthly shipping cost. b. Plot the errors for the predictions in order of time sequence. Is there any unusual pattern? c. It turns out that there was a trucking strike during months 11 through 15, and you believe that this might have influenced shipping costs. How can the answer to part a be modified to account for the effect of the strike? After accounting for this effect, does the unusual pattern in part b disappear?