Answer
Next year, the salesman will have to sell 161 cars.
Work Step by Step
Let X represent the amount of cars the salesman will have to sell next year.
A guideline for this problem would be:
Next year sales = This year sales + Increase in sales
So, X = 140 + 140 $\times$ 15%
X = 140 + 140 $\times$ .15
X = 140 + 21
X = 161
Next year, the salesman will have to sell 161 cars.