The key here is to look at the units digits.
If you look closely, you'll notice that we have a situation where triangle * square = square.
Thus, we know that triangle must be equal to 1. (It helps to know that triangle * square is less than 10, as they tell us in the problem)
This narrows our answer choices down to A, D, and E.
A is ruled out because we know that the dist must be different, and two ones don't count as different.
Thus, we want to test 21 and 32.
21 * 12 = 252 ==> this seems to fit the pattern. Notice that the square here represents a 2, and that the answer has 2's as the hundreds and units digit, as in square-diamond-square.
31 * 13 = 403 ==> this one doesn't fit the pattern. We want something that looks like square-diamond-square, and 403 has different digits in the hundreds and units places.
Thus, our answer is D.