The following cumulative relative frequency distribution summarizes data obtained in a study of the ending overages (in dollars) for the cash register balance at a business:

a. Determine the proportion of the days in which there were no shortages.
b. Determine the proportion of the days the cash register was less than $20 off.
c. Determine the proportion of the days the cash register was less than $40 over or at most $20 short.