Question

Rosy has two faulty alarm clocks. Clock A rings every six hours, and Clock B rings every nine hours. when will they both ring together for the first time?

Choices

A. after 6 hours
B. after 9 hours
C. after 15 hours
D. after 18 hours

I need this done ASAP. First one to answer will definitely get a thx.
Please and thank you

Answer 1

Take each answer, and see which number of hours is divisible by 6 and 9. 6,9,and 15 are not divisible by both numbers. Only 18 can be divided by 6 and 9, so the answer is D.