How I do it is first, you look at the number that is in the hundreds place. Then you look at the number behind it. If the number is 5 and above, you make the number in the hundreds place grow one number (7 would become 8), and you turn the 6 into a 0. If the number is 4 and below, you keep the 7 and turn the other numbers into 0s (7 would stay 7, and 8 and 6 would become 0s).
