In 2013, A got 27% of its revenue through LIG housing whereas in the same year B earned 42% of its revenue through MIG housing. Both the companies spent ₹350 crore less than these revenues obtained. The difference in percentage profits thus earned by A and B is .........

Firm A's revenue in 2013 is 3150 crores.

Given 27% of these came from LIG i.e. $$3150\times\dfrac{27}{100}=850.5$$

It spent 350 crores less than this

So, the profit percentage is $$\dfrac{350}{850.5}\times100=41.15\%$$

Similarly, 

Firm B's revenue in 2013 is 5070 crores.

Given 42% of these came from MIG i.e. $$5070\times\dfrac{42}{100}=2129.4$$

It spent 350 crores less than this

So, the profit percentage is $$\dfrac{350}{5070}\times100=6.9\%$$

Hence, the difference in profit percentage is 41.15 - 6.9 = 34.24%

So, the answer is Option B.