By definition, government expenditure refers to the money used in the acquisition of goods and services for current use. In this case, the government expenditure is simply equivalent to investment.
Government expenditure = $400 billion
From economics: I=S+T–G+M–X
Where
I = Investment
S = Savings
T= Tax revenues
G =Government budget
M = Import
X = Export
Rearraging to get G:
G = S – I + T + M – X
G = $400 billion - $400 billion + $500 billion + $200 billion - $300 billion
G = Government budget = $400 billion