Answer:
Change in government expenditure needed = 300 
Step-by-step explanation:
Multiplier 'k' = Change in Income / Change in Govt. expenditure = dY / d GE = 1 / ( 1-MPC ) 
Desired change in Y, ie GDP = 900 billion , MPC = 2 / 3. 
k = 1 / ( 1 - 2/3 ) = 1 / ( 1/3 ) = 3 
3 = 900 / d GE 
d GE = 900 / 3 = 300 
Change in government expenditure = 300