d) What is the value of unplanned changes in the inventory investment when real GDP is $4000? e) What is the size of the multiplier in this economy? f) If investment spending increases by $50, what would be the value of the change in the equilibrium real GDP?

I got this one wrong, could you tell me the correct one? thank you

Aa30  Economics

Consider two closed economies that are identical except for their marginal propensity to consume (MPC). Each economy is currently in equilibrium with real GDP and total expenditure equal to $100 billion, as shown by the black points on the following two graphs. Neither economy has taxes that change with income. The grey lines show the 45-degree line on each graph. The first economy's MPC is 0.5. Therefore, its initial total expenditure line has a slope of 0.5 and passes through the point (100, 100). The second economy's MPC is 0.70. Therefore, its initial total expenditure line has a slope of 0.70 and passes through the point (100, 100). Now, suppose there is an increase of $30 billion in investment in each economy.   Place a green line (triangle symbol) on each of the previous graphs to indicate the new total expenditure line for each economy. Then place a black point (plus symbol) on each graph showing the new level of equilibrium output.