The number that was supposed to fill in the blank is missing. But since the
product of all three must be 30 and the one's digit is 3, the product of the
first two digits must be 10, so that when that is multiplied by the one's
digit the product will be 30. The only two digits which have product 10 are 2
and 5. So the answer is either 253 or 523. The number that was supposed to
fill in the blank then has to either be 5 or 8. If a 5 was supposed to fill
in the blank, then the answer is 523, and if an 8 was supposed to fill the
blank, then the answer is 253.