Answer:
Step-by-step explanation:
The two dump intervals have a greatest common factor (GCF) of 3, so their least common multiple (LCM) is ...
(18)(21)/3 = 126 . . . . minutes
This period is 2 hours 6 minutes. The last time both dumped was 1:10, so the next time both will dump is ...
1:10 +2:06 = 3:16 . . . P.M.
and the next time after that is ...
3:16 +2:06 = 5:22 . . . P.M.