Answer: It would take 25 days, so C is the answer.
Explanation:
We know that Petra walks her dog for 2/5 mi each day. We want to know how long it would take them to walk 10 mi. In order to solve this, divide 10 by 2/5
[tex]\frac{10}{1} ÷ \frac{2}{5} = \frac{10}{1} * \frac{5}{2} = \frac{50}{2} = 25
Just use basic fraction division :)