Could someone me understand this?

How many $20 bills do you need to have to make $280

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

For what type of equity loan are you lent a lump sum, which is to be paid within a certain period of time? a. a line of credit b. equity c. a second mortgage d. an amortization