We have to find the least number of flowers that can be arranged equally in 5, 6 or 9 rows.
It can be found out by calculating the least common multiple of all three numbers.
Multiples of 5 = 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100.
Multiples of 6 = 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84, 90, 96, 102.
Multiples of 9 = 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99.
We can see that 90 is the least common multiple of given numbers.
Hence, the least number of flowers which can be planted are 90.