In order to do this, we can use our squares. We know that 15^2 is equal to 225, so 15 has to be part of the answer. However, the answer is negative, and the one of the given numbers to multiply with is negative. But, if we multiply a negative number by a negative number, we get a positive number, which means that the missing number must be positive. Therefore, our answer is 15.
Hope this helps!
