Stephen has art lesson every 6 days.And a swim lesson every 9 days.He has both art and swim lesson on Tuesday.On which day of the week will he have both lessons again?
The least common multiple would give you the answer you are looking for.
Multiples of
6: 6, 12, 18, 24, 30, .....
9: 9, 18, 27, 36, .....
He will have a lesson on the same day in 18 days.
Starting on Tuesday we need to go 18 days. 14 days would be another Tuesday, Wednesday = 15, Thursday = 16, Friday = 17, Saturday = 18