Answer:
15 days
Step-by-step explanation:
Since he used both of the weights today, he will only do both on the day they come together.
weights: 3 days, 6 days, 9 days, 12 days, 15 days
machine: 5 days, 10 days, 15 days
Because the numbers both were the same on 15 days, then that is when he will do both of them
