Someone help me please

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?

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

Two variables, x and y, vary inversely, and x=12 when y=4. what is the value of y when x=3?