Two lighthouses can be seen from the top of the hill the first flashes once every six seconds and the other flashes once every 15 seconds if they flash how long is it until they flash again at the same time

30 seconds

Step-by-step explanation:

Find the least common multiple of 6 and 15.

First, write the prime factorizations.

6 = 2 * 3

15 = 3 * 5

The LCM is the product of each distinct factor.

LCM = 2 * 3 * 5

LCM = 30

They flash together at the same time every 30 seconds.