(I apologise since i didn't understand the question very well, but here's what i think it means)
Answer = 45 people.
If Bob can only make a sale to every third person, then in order to make 15 sales he needs to multiply 15×3 in order to get the number 45. Which means, that in order for Bob to make 15 sales he needs to talk to 45 customers.
- Hope it helps!
