The number of divisors of 10800 which are divisible by 15, is 

We have, $n=10800=2^4\times 3^3\times 5^2.$

A divisor of 1nvill be a multiple of 15, if it contains at least one 3 out of three 3's and at least one 5 out of two 5's. Hence, the number of divisors which are multiples of 15 is equal to ( 4 + 1) ( 3) (2) = 30 .