Average Number of Dogs Sold

A pet store regularly tracks the number of different kinds of pets sold each week. Over the last five weeks, the sales data is as follows:

Week 1: 8 cats, 5 dogs, 2 birds

Week 2: 7 cats, 6 dogs, 4 birds

Week 3: 10 cats, 8 dogs, 5 birds

Week 4: 9 cats, 5 dogs, 3 birds

Week 5: 11 cats, 7 dogs, 6 birds

What is the average number of dogs sold per week over the five-week period?