Please help...

Will someone please help on the questions circled in black...

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 perimeter of a stage is 116 feet. it is 17 feet wide. how long is it?

Solve the system of equations. x=-2y+1 and x+2y=9. show work