Answer:
He will have earned $119.25
Explanation:
If Brian is charging $4.50 per single dog and he walks 13 dogs. 13 times $4.50 is $58.50...
If Brian charges $6.75 per set of dogs, and he walks 9 sets, 9 times $6.75 is $60.75...
If we add those together we end up with $119.25