How many positive integers less than 10,000 are such that the product of their digits is 210?
(A) 24
(B) 30
(C) 48
(D) 54
(E) 72
210 = 2*3*5*7.
So the numbers have to be made of above four digits.
If we take all 4 primes as separate digits, then 4*3*2*1 = 24 different numbers.
We can also make numbers from the digits 6 (2*3), 5 and 7 = 3*2*1 = 6 different numbers so total 30 numbers.
Hence the answer is B