Can anyone help me on this pls and ty

Cassie is traveling 675 miles today to visit her brother and his family. so far, she has stopped for gas three times. at the first stop, she put in 7.1 gallons of gas and paid $23.79. at her second stop, she put in 5.8 gallons of gas and paid $19.08. and, at the third stop, 6.6 gallons and paid $20.39. at which stop did casey pay the most for gas?

The anwser cause i do not understand just plez

When i'm with my factor 5, my prodect is 20 .when i'm with my addend 6' my sum is 10.what number am i