Alright, so she drives 64.5*5 (for 5 days)=322.5 miles each week. She then uses 322.5miles/1 * 1gallon/21.5 miles (we have 1 gallon/21.5 miles because 1 gallon=21.5 miles and we have the gallon at the top to cross the miles out)=15 gallons. The cost per gallon is 2.85 (we add 2.85 for each gallon), and we have 15 gallons, so 2.85dollars*15l=42.75 dollars is our answer
