Problem Solving - Shore Lights

An observer on a boat on Port Phillip Bay at night can see three different shore lights. The red one winks every 6 seconds, the white one every 10 seconds and the green one every 14 seconds

a. How often do the red and green lights wink on together?

b. How often do the green and white lights wink on together?

c. How often do the red and white lights wink on together?

d. How often do all three lights wink on together?

The observer notes that at midnight the red and white lights wink together. Six seconds later the green, and obviously the red, light wink on.

e. When will they all next wink together?

f. When will this next occur exactly on the hour?

I am having trouble working out this problem can someone please help me thanks.