Giving 18 point plz plz help

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?

What is the domain of the step function f(x)=[2x]-1?

Oliver makes blueberry jam every year. the number of kinds of jam he makes this year can be represented by the expression 4p -9, where p is the number of pints he made last year