5 years, annual interest rate 10%. Now it can be converted into 7.5 yuan at the exchange point stipulated by the state; Hello! 1987 5 yuan's treasury bills were exchanged in 7.5 yuan, and the reference price in the collectible market was 16-25 yuan/Zhang (new product). However, since this kind of treasury bill has exceeded the redemption period, no commercial bank can redeem it. Generally, you have to go to the local people's bank to exchange it. In some areas, the People's Bank of China can designate 1 and the central branches of two commercial banks for fixed-point exchange. You need to change money in these places. However, because treasury bills are overdue without interest, even if they are overdue for a long time, there is still only interest due. Therefore, if it is not cost-effective to exchange good quality treasury bills, they can be sold in the local postal currency card market, and the price is definitely higher than that of the exchange. 1987, the face value of national debt 10 yuan, and the market price of postal currency card is 35 yuan; 1987, the market price of 50 yuan's national debt and postal currency card was 2,700 yuan; 1987 national debt face value 100 yuan, and the market price of postal currency card is 4000-4200 yuan;