What is the sum when the two decimals are added together

How do i do this? i don’t understand

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?

Percy rides his bike 11.2 miles in 1.4 hours at a constant rate. write an equation to represent the proportional relationship between the number of hours percy rides, x,and the distance in miles, y, that he travels.