Given information:
- Principal amount borrowed: Rs 5000
- Time period: 2 years
- Interest rate on borrowing: 4% per annum
- Interest rate on lending: 6% per annum

Calculation of interest on borrowing:
To calculate the interest on borrowing, we can use the formula:

Interest = (Principal * Rate * Time) / 100

Substituting the given values, we get:

Interest = (5000 * 4 * 2) / 100
= Rs 400

Calculation of interest on lending:
To calculate the interest on lending, we can use the same formula:

Interest = (Principal * Rate * Time) / 100

Substituting the given values, we get:

Interest = (5000 * 6 * 2) / 100
= Rs 600

Net gain:
To find the net gain, we need to subtract the interest paid on borrowing from the interest earned on lending:

Net gain = Interest earned - Interest paid
= 600 - 400
= Rs 200

Explanation:
The person initially borrows Rs 5000 for 2 years at an annual interest rate of 4%. This means that after 2 years, he will have to pay back the principal amount of Rs 5000 plus an additional Rs 400 as interest.

However, instead of using the borrowed money for his own purposes, he immediately lends it to another person at an annual interest rate of 6%. This means that after 2 years, he will receive the principal amount of Rs 5000 back from the borrower, along with an additional Rs 600 as interest.

Therefore, the person's net gain in this transaction is Rs 200, which is the difference between the interest earned on lending (Rs 600) and the interest paid on borrowing (Rs 400).

Conclusion:
In this transaction, the person gains Rs 200 by borrowing money at a lower interest rate and lending it at a higher interest rate.