You own a cell phone company and need to determine the plan you will use to charge your customers each month. Write an equation for a cell phone plan that charges a flat fee plus a fee per 50 MB of data each month. For example, your plan might be $20 plus $5 per 50 MB of data used during the month.. Choose a flat fee between $5 and $25, and choose a rate for data between $1 and $20 per 50 MB used.