If r◼s = 3r + s, find 4◼(2◼1).
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U should have subtract 180 and 131
Every number will have only 3 digits. In the ones place, there are 5 choices. For every choice of digit made in the ones place, there are 8 possible choices for the hundreds place (you can choose from 1-9, omitting whatever is used in the ones place), and there are 8 possible choices for the tens place (you can choose from 0-9, omitting whatever has already been used elsewhere).
So there are
such numbers.
So there are