Please answer this correctly

If eh = hg and hg=16, find the diameter of k

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?

Translate this phrase into an algebraic expression. 21 more than twice goran's savings use the variable g to represent goran's savings. need to know fast.