National income at market price is higher than national income at factor cost by what amount?

(indirect taxes -subsidies)

The correct answer is Option 4: (indirect taxes -subsidies)

NNP_FC = National Income (NI ) = NNP_MP –(Indirect taxes – Subsidies).

The products which we receive in market are the one's which already include the effects caused on price due to subsidies given by the govt and imposition of indirect taxes. This term is also known as NNP_MP. 
NNP_FC is the price of the product which includes the cost associated which its production as the name suggests FC i.e. Factor cost. Now in order to move from FC to MP we need to make adjustments of indirect taxes imposed and subsidies given.
NNP_FC + indirect tax - subsidies = NNP_MP ( We added indirect tax as imposition of indirect tax would raise the price of the product and subtracted subsidies because when government gives subsidies it reduces the cost of production. For ex. loan given on subsidized rate to the producer.)
We can also say that:
NNP_MP - indirect tax + subsidies = NNP_FC (Unitary method)
This can also be understood as if from the market price of the product the component which has caused increase in price (indirect tax) is deducted and the one which has reduced the price (subsidies) is added to reach at the price at FC.
We can also write the above statement as :
NNP_MP - (indirect tax - subsidies) = NNP_FC.
Therefore, it can be concluded that NI at MP is higher by (indirect tax - subsidies ) when compared with FC.