Answer
15
Work Step by Step
The sales in the 9 weeks are 12,13,13,14,14,14,15,15,15,15.
You multiply 14 and 10 to find the total number of sales needed to average 14 over 10 weeks.14 $\times$10=140. Add the sales of 9 weeks:12,13,13,14,14,14,15,15,15,15=125. Subtract the current sales from 140 to find how many sales are needed on the 10th week:140-125=15.You need to make 15 sales in the 10th week