Final answer:
To counteract a $200 billion decrease in aggregate demand with an MPC of 0.7, the government would need to implement a fiscal stimulus package worth $60 billion to bring AD back to its original level. Therefore, the correct option is b. $60 billion.
Step-by-step explanation:
The student has asked about the appropriate size of a fiscal stimulus package to offset an adverse demand shock that decreased aggregate demand (AD) by $200 billion, given a marginal propensity to consume (MPC) of 0.7. To calculate the size of the fiscal stimulus, the spending multiplier is used, which is calculated as 1/(1-MPC). In this case, the spending multiplier would be 1/(1-0.7) = 3.33. Therefore, to offset the decrease in AD by $200 billion, the government would need to spend $200 billion divided by the spending multiplier, which would be $60 billion. Thus, the correct answer is b. $60 billion.