The difference between a hundred and a number is four times that number

20

Step-by-step explanation:

We know that the difference between a hundred and a number is four times that number.

So assuming the number to be x, we can write the difference between a hundred and a number as 100 - x and four times that number as 4x.

So by combining these together, we get:

100 - x = 4x

100 = 5x

x = 100/5

x = 20

Therefore, the unknown number is 20.

Easy :).

Remove the flat rate to see how much money she has to spend: 10 - 1.95 = 8.15.

We have 8.15 (remaining money) / 0.60 (per mile) = 13 miles (or 13.5833333333 [copy pasted from a calculator moderators] but I assume you want a rounded version)