VB 2008 Code The Calculations For A Pocket PC Application That Calculates The Cost Of A Cell Phone Bill?

I'm having trouble figuring how to code the calculations for a Pocket PC application that calculates the cost of a cell phone bill. From a Pocket PC the user should enter the number of minutes used during the past month, in order to calculate the cost of the cell phone bill. The plan allows 300 minutes for $29.95 per month. For each minute over 300 the cost is $0.17 cents per minute. Tax and Fees are $4.85 a month.

1. User enters the number of minutes used during the past month.

2. Based on plan rate of 300 minutes for $29.95 and 17 cents for each minute over 300 calculate the cost of the bill including the fixed cost of $4.85.

3. The user must be able to initiate the calculation and display the individual charges and the total cost of the cell phone bill.

4. The user should be able to clear the number of cell phone minutes, the individual charges and the bill total

If negative number is enterd for the cell phone minutes, the user should be advised and asked for a valid entry If non numeric value entered for the cell phone minutes, or if left blank the user should be advised and asked for a valid entry.Application is deployed on the Pocket PC emulator built in VS 2008

Enter # of Minutes ________ (user enters)
Regular Minutes Charge ___ (29.95)

[code]....