Jenny Was Reviewing the Water Bill for Her Doggy Day

Jenny was reviewing the water bill for her doggy day spa and determined that her highest bill, $1,700, occurred in July when she washed 800 dogs and her lowest bill, $900, occurred in November when she washed 400 dogs.
- What was the variable cost per dog associated with Jenny's water bill?

A) $0.67
B) $1.00
C) $0.50
D) $2.00