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.

me with this problem, i don’t understand it. in advance! : d

It seems confusing, but it's just breaking down the steps for you. It's done the same as any other word problem.
a. The unknown is how many minutes she used beyond the plan. So, we'll use "m" for the variable, to represent minutes.
b. 73.40 = 65 + 0.10m
   The 73.40 is the total, which is why it's by itself. 65 represents the price per month for the plan, and 0.10m is the price per extra minute multiplied by the unknown amount of minutes used.
c. 73.40 = 65 + 0.10m
     8.40 = 0.10m
       84 = m
d. The number of minutes that Allegra went over the time that the plan allows is found by solving the equation we just wrote and solved. $0.10 is paid for every minute past the plan's allowance, meaning that "m" in the equation, when solved, shows us exactly how many minutes over Allegra went.