Let a, b, and c be the digits of X. Then we know the following:

ab >= 16
bc >= 35
abc = 72

Also, since the product of the digits is 72, we know none of the digits are either 5 or 7.

Since ab >= 16 and bc >= 35, then ab²c >=560.

But since abc = 72, we can divide these two equations to obtain:

b > 7

Thus the middle digit is either an 8 or a 9.

If the middle digit is 8, then the first digit has to be either 2 or 3 (to make the product fall between 16 and 24) and the last digit has to be 5 or 6 (to make the product fall between 35 and 45). So the possibilities with 8 as the middle digit are: 285, 286, 385, and 386. But none of these give a digit-product of 72.

If the middle digit is 9, then the first digit must be 2, and the last digit must be 4 or 5 (using reasoning similar to that above).

Thus, with 9 as the middle digit, the possibilities are: 294, and 295.

Since 2 x 9 x 4 = 72, the only answer is: 294