Rounding to estimate the difference of 18.14 - 9.88

18.14 rounds to 18 because you look at the 1 and (0, 1, 2, 3, 4) tell you to round down. That means 18.14 rounds down to 18

9.88 rounds to 10 because you look at the first 8 and (5, 6, 7, 8, 9) tell you to round up. That means 9.88 rounds up to 10.

Now it's just simple math. 18-10 = 8