Please help im so confused

Average salary for a medical assistant is $31,220 which is a 20% income tax bracket how much money would they pay in income tax?

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?

Ms.lopez has 4 liters of chemicals that she is going to pour into beakers. each beaker will have 1/4 of a liter of chemicals, how many beakers can ms.lopez fill? draw a model to support your work. (it's ok if you dont)