One inlet pipe can fill an empty pool in 12 hours in a drain can empty the pool in 15 hours. How long will it take the pipe to fill the pool if the drain is left open? 

15 *12 is equal to 180 mark me brainlist

(n^3 - n)

= n(n-1)(n+1)

since it is divisible by 3 and 2 ,because it is a multiple 3 consecutive number

if, n-1 is odd then n+1 is also odd, then it is a multiple of 9

but if, n-1 is even then n+1 is also even, then it is a multiple of 4

so, largest multiple = max(9*2, 4*3) = max(18, 12) = 18