Sam's Lawn Service uses the equation, y = 15x + 25 to calculate the cost, y, to work on a customer's lawn for x number of hours.
Ron's Lawn Service uses the table below to calculate the cost to work on a customer's
lawn.

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?