We shall first of all, convert all the numbers to the same base. This means we either;
Convert the fractions to decimals OR
Convert the decimals to fractions
Let us therefore convert the decimals to fractions.
You want to be finding out what two factors (where one of them is a perfect square) has the produce of 63. It seems like 9 x 7 (9 is the perfect square) works.

The square root of 9 is 3 so we can just have

(which just means 3 times the square root of 7).
400/2 = 200
200 + 20 = 220
200 - 20 = 180
Answer: He had gone 220 miles.
He was 180 miles from the finish and 220 from the start, so he was 40 miles closer to the finish than to the start.