Calculate the change in real GDP that would result in each of the following cases, assuming there are no automatic stabilizers or destabilizers.
a. Planned investment spending rises by $100 billion, and the MPC is 0.9.
b. Autonomous consumption spending decreases by $50 billion, and the MPC is 0.7.
c. Government purchases rise by $40 billion, while at the same time investment spending falls by $10 billion. The MPC is 0.6.