Answer:
1. Fall; Increase
As a result of a lower tax rate on interest income, more people will be encouraged to save because their earnings from savings will be more. This will increase the amount of loanable funds in the economy and when Supply is higher, prices drop. This is why interest will fall. The level of investment spending which is savings, will as earlier mentioned, increase.
2. Rise; Rise
As a result of the new tax credit on investment, companies will.want to invest more and buy more capital goods. This will lead them to acquire more loanable funds to finance the investments. This increases the demand for loanable funds thus shifting the demand curve for loanable funds to the right. As a result of this increase in demand, the interest rates will rise because more entities want loanable funds and according to Economics when demand rises, prices rise. The interest is the price in this scenario.
Investment evidently rises.
3. Surplus; Increases
The Government budget was balanced meaning that Expenditure equaled Revenue. The War ends and the Government reduces defense spending which means that Expenditure decreases yet Revenue remained the same. Revenue is now more than Expenditure meaning that the government has more money that it is spending which is a Surplus.
This will increases National Saving because the Government channels it into the Economy.
4. Fall; increasing
As a result of more savings in the economy, loanable funds increase which will shift the supply curve for loanable funds to the right. This will lead to a fall in interest rates. This fall in interest rates will encourage companies to take advantage of the lower rates and acquire more loans to invest which will increase Investment spending. I attached a graph to demonstrate.