Mehrotra said the additional rate for PC flash drives in 2017 is about 35 percent, and will increase to 75 percent by 2020. And "a lot of hard drives still need to be replaced by SSDS... Future self-driving vehicles are expected to be equipped with about 40GB of DRAM... This will also drive the use of NAND flash memory." The average interest rate on fixed-rate bonds has also increased. According to data firm Moneyfacts, the two-year average bond rate has risen by 41 percentage points, while the average price of three-year bonds has risen by 32 percentage points, as shown below. According to this model, the interest rate decision depends on the supply of savings and investment needs, money supply, money demand, four factors, cause a change in the saving investment, money supply and demand factors will affect the level of interest rates. This theory is characterized by general equilibrium analysis. Profit is not only the same in quality, but also the essence of profit. Profit is the form of corporate profit, and is also equal in quantity. The difference in profit is that for variable capital, profit is for all costs. Once earnings into profits, therefore, the origin of profits and material production is made it is a reflection of the "(" the complete works of Marx and Engels in volume 25, page 56), and thus has the various forms of money. In capitalist society, the essence of profit is: it is the product of capital, it has nothing to do with labor.