If 12 people are needed to run four machines, how many people are needed to run 20 machines?

Find the number of people to run one machine:

12 people  /  4 machines = 3 people per machine.

Now multiply the number of people needed for 1 machine by the total number of machines:

3 people x 20 machines = 60 total people needed.

These are the multiples of 15 but what you are probably asking or what are the factors of 15