Problem Solving

Hi, can anyone help me to solve this question??


Month Numbers of Days worked

June 20
July 17
August 19

The table above shows the number of days worked by a certain sales representative in each of the three months last year. If the number of sales call that the representative made each month was proportional to the number of days worked in that month and if the representative made a total of 168 sales calls in the last 3 months shown, how many sales calls did the representative make in august?

A) 50
B) 51
C) 56
D) 57
E) 60

Answer[spoiler] (D)[/spoiler]

From this given information:
If the number of sales call that the representative made each month was proportional to the number of days worked in that month
It can be assumed that the sales representative makes the same average call per day each month.
Average call per day for 3 months: 168/(20+17+19) = 3
No. of calls made in August: 19 *3 = 57.
Pick D.