She drove 700 miles during the 3-day period.
Work Step by Step
Let X represent the number of miles she drove during the 3-day period. The agency charges 25 dollars per day, so she paid 3 $\times$ 25 = 75 dollars. Also, the agency charges 0.20 per mile. Since she drove X miles, she paid 0.20 $\times$ X = 0.20X. The total amount she paid was 215 dollars. We set up the following equation: 75 + 0.20X = 215 0.20X = 140 Divide both sides by 0.20. X = 700. She drove 700 miles during the 3-day period.