To find this answer, you must first find out how much money he made for walking dogs on Tuesday. To do so, multiple 8 (number of dogs) by 3 (amount of money earned per dog. This will give you 24, which you subtract from the total (45). 45 - 24 = 21. Finally, divide 21 (amount he made on Monday) by 3 (amount of money earned per dog) to get 7 dogs on Monday.
