How do i get a better grade if i'm failing

What is the volume of a rectangular prism that is 120 centimeters by 2 meters by 1.5 meters in cubic meters?

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?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie