I need help ;-;.

9

Step-by-step explanation:

divide 15 by 5 to get the scale factor ( this work is related to scale factors)

= 3

then to find a, multiply 3 by 3(scale factor) to get 9

idk do it yourself or ask somebody idk stop going online asking for

(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