Number of roses 3 6 9 12 15
Price (dollars) 9 18 27 36 45 . Find the cost of purchasing 30 roses

90

Step-by-step explanation:

multiply 30 by 3

(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