Basically, National income can be calculated as follows:
National Income = GDP - Private consumption of fixed capital - Government consumption of fixed capital
Now as,
GDP = C + I + G + (X - M)
Where, I = Gross private domestic investment
Now with the increase in the Private investment spending, there will be an increase in National Income. Moreover, Investment has a positive relation with national income and negative relation with interest, therefore, when investment will increase, income will go up.
National Income = GDP - Private consumption of fixed capital - Government consumption of fixed capital
Now as,
GDP = C + I + G + (X - M)
Where, I = Gross private domestic investment
Now with the increase in the Private investment spending, there will be an increase in National Income. Moreover, Investment has a positive relation with national income and negative relation with interest, therefore, when investment will increase, income will go up.