You've got the right set up for this problem. Now you just need to subtract the decimals. The rules of borrowing from the left for a column on the right work with decimals too. Borrow from the tenths column and put it in the hundredths column.
22.3 10
-21.8 1
9
Repeat with the tenths column
21. 13
21. 8
5
Since 21 - 21 = 0, We keep the decimal place and the rest. Thus 22.40 - 21.81 = 0.59
Thus Tom swam 0.59 seconds slower in 1985.
