rules of profit maximization As the center of global automotive engine research and development and production, Britain's powertrain design has always maintained the world's leading level, especially in engine design. In 2013, the UK produced 2.55 million engines, accounting for 30 per cent of total European engine production, with 62 per cent of the engines exported to more than 100 countries. The difference between the income and the total income has been realized In this way, if the interest rate of a country is higher than that of other countries, it will attract a large amount of capital inflow, and the outflow of funds from the country will decrease, leading to the buying of this currency in the international market. At the same time, the capital account balance has been improved, and the currency exchange rate has been raised. On the other hand, if a country is loose credit, interest rates fell, if interest rates lower than in other countries, can cause large capital outflows, foreign capital inflows to reduce, the capital account balance of payments deteriorates, while selling the currency in foreign exchange market, caused the exchange rate to fall.