Financial Modeling

We are completing a model in excel to determine working capital required to run operations and amount of capital required to acquire devices. Most of the model has been completed but we need help with some if/then formulas. There are two product lines, (post paid and prepaid), that has been consolidated to determine the total cash requirements. However, we need help with if/then statements to look at the cash balance and balance available on the credit facility. In addition, I would like help with my borrowing base computaion for the line of credit. One last part of the exercise are some slides sumarizing the model.