Answer: She paid the most for the gas in the first stop ($3.35 per gallon).
Step-by-step explanation:
1. At the first stop she put in 7.1 gallons of gas and paid $23.79, so she paid:
$23.79/7.1 gallons=$3.35 per gallon.
2. At her second stop she put in 5.8 gallons of gas and paid $19.08, then the price per gallon was:
$19.08/5.8 gallons= $3.28 per gallon.
3. At the third stop she put 6.6 gallons and paid $20.39, then:
$20.39/6.6 gallons=$3.08 per gallon.
4. Then, you can conclude she paid the most for the gas in the first stop ($3.35 per gallon).