We have to find the least common multiple of 6 and 9.
Multiple of 6 = 6, 12, 18, 24, 30, 36, 42, 48, 54... [1 mark]
Multiples of 9 = 9, 18, 27, 36, 45, 54, 63, 72, 81... [1 mark]
18 is the least common multiple of 6 and 9.
So, they will meet again, next after 18 min. [1 mark]