When comparing two numbers, there are a few different things you might be interested in: which is larger, which is smaller, or whether they are equal.
In this case, we can see that both numbers are negative, which means they are to the left of zero on the number line. In general, the further left a number is on the number line, the smaller it is. Therefore, we can say that:
-2.25 > -3
In other words, -2.25 is larger (closer to zero) than -3.