1. allegra has a cell-phone plan that charges $65 per month and $0.10 for every minute that she uses the phone beyond what her plan allows. one month, she was billed $73.40. (a) define a variable for the unknown. (b) write an equation to model the problem. explain your answer. (c) solve the equation. show your work. (d) find the number of minutes that allegra went over the time that the plan allows. explain your answer.