One light flashes every 2 minutes and another light flashes every 3.5 minutes. Suppose both lights flash together at noon. What is the first time after 1 PM that both lights will flash together ?

2 4 6 8 10 12 14 16 18 .....

3.5 7 10.5 14 17.5 ...

looks like they are together (in sync) at
12:14 12:28 12:42 12:56 1:10 1:24 ....

so the first time after 1:00 will be at 1:10