Answer:
20,000 pairs of barber scissors.
Explanation:
The sales volume V for barber scissors is directly proportional to the size S of the sales force and inversely proportional to the price P of the scissors.
In other words, we can write that:

Where k is the constant of proportionality.
19,440 pairs were sold in 2013, when there was 54 salespeople and the price was $20 a pair. Hence, V = 19440 when S = 54 and P = 20. Substitute and determine the value of k:

Hence, our equation is:

We want to determine the sales forecast with 50 salespeople and a price of $18 a pair. Hence, S = 50 and P = 18:

In conclusion, 20,000 pairs of barber scissors can be expected to be sold.