Forecasting balance sheet items : short term investments and short term borrowings

Hi there, I have to project short-term investments and short-term borrowings for a manufacturing company. I have projected all other items based on relevant parameters. I am currently facing issue how to adjust the balance sheet based on the two accounts. Should I keep short-term investments as a balancing figure (what about the cash then??). And if so then how to forecast short-term borrowings?? I thought of making use of debt to equity ratio (deriving short-term borrowings from the % of debt to equity) keeping in view the past trend (and its decreasing) but even so, my valuation gets disturbed..... how to justify the optimal figure??

THANKS IN ADVANCE