According to the title, the cash yield is y, and the financing cost is ra and Rb. Because the question does not give specific information, it is assumed that Ra is the loan interest rate and Rb is the loan interest rate. For non-bank institutions and individuals, Rb >；; Ra. Then the holding cost is an interval, namely [Ra-Y, Rb-Y].

Through the futures pricing formula, it can be concluded that the futures price F lies in an interval, namely [PE (Ra-y (t-t)) and PE (Rb-y (t-t)].

We can use the concept of holding cost to solve the calculation problem of forward and futures prices. Composition of holding cost:

Holding cost = storage cost+interest cost-income provided by the underlying assets during the contract period.

C stands for holding cost, and the price is: F = PE C (T-T).