Walter and his parents are a little unusual. If he does an acceptable job of doing his chores, he gets paid 3.33 dollars for that day. If he does an outstanding job, he gets 3 dollars more. During one 10 day period, Walter received 42 dollars and 30 cents for his work. How many days did Walter earn the extra money?
3.33*10+3E=42.30
3E=42.30-33.3=9
E= 3 days.