Answer
Investment equals B) $500
Step-by-step explanation:
We first lay out the national income identity in this form:
Y-C-G = I + NX
Where:
Y-C-G = National Saving
I = Investment
NX = Net exports (when NX is posivite, the economy is running a trade surplus).
National Saving = Private Saving + Public Saving (Tax revenue minus Government spending ($400 - $300))
National Saving = $500 million + $ 100 million
National Saving = $600 million
Now we plug the amounts into the identity =
$ 600 million = I + $ 100 million
We rearrange terms
$600 million - $100 million = I
$500 million = I
So, Investment is $500 million