this is a problem that should be thought through logically not mathematically. There are 7 days in a week. The average should be 4. To get there it should be x ÷ 7 = 4 or 4 × 7 = x so 28. the total for the week should be 28 miles and before saturday it is 20.5, so we need an additional 7.5 miles to be a 4 mile average.
