Question 892609
the remaining balance in your account  for every transaction period is the remaining balance in your account from the previous transaction period minus the cost for this transaction period.



let m = minutes of use.
let c = cost per minute of use.


total cost for the current transaction period is m*c.


this assumes no other costs except the cost for minutes of use.


let b1 = the balance in the account from the previous transaction period.


let b2 = the balance in the account for the current transaction period.


your formula becomes:


b2 = b1 - m*c