Final answer:
In equilibrium, the real interest rate adjusts to equate desired national saving and desired investment. The actual values would depend on the real GDP and other provided figures in the Keynesian cross model.
Step-by-step explanation:
If the goods market is in equilibrium, then the values of the real interest rate, desired national saving, and desired investment are such that the level of saving equals the level of investment. This is in accordance with the national saving and investment identity, which states that in an economy, an individual's income not used for consumption or government taxes becomes savings, which should be equal to the investments made within that economy. In the given scenario where the marginal propensity to save is 0.1 and taxes are 0.2 of real GDP, with a fixed level of investment of $70, the equilibrium real interest rate will adjust to ensure that saving equals investment. The exact figures depend on the real GDP of the economy. The national desired saving and investment would thus reflect the equilibrium values where the supply and demand for financial capital balance each other, given the levels of government spending, consumption, exports, and imports provided in the Keynesian cross model.