3 litters were born last year and each litter had 7 puppies how many puppies were born last year

3 litters, 7 puppies in each litter, 3 x 7 = 21 puppies last year

In this situation, you are finding how many puppies per litter. you know that there are 3 litters, and that there are 7 puppies per litter, so if you add 7 three times, you get 21. another way you can find it is that you multiply 7*3=21