Answer : 3. "20%"
Explanation :

To find the profit or loss percentage, we first need to calculate the cost price (CP) and the selling price (SP) of the bananas.

Given: Cost price of 6 bananas = ₹ 15 So, cost price of 1 banana = ₹ 15 / 6 = ₹ 2.50

Now, let's calculate the selling price: Selling price of 4 bananas = ₹ 12 So, selling price of 1 banana = ₹ 12 / 4 = ₹ 3.00

Now, we can compare the CP and SP to determine the profit or loss.

If SP > CP, it's a profit. If SP < CP, it's a loss.

Here, CP = ₹ 2.50 SP = ₹ 3.00

So, it's a profit of ₹ 0.50 per banana.

To find the profit percentage: Profit per banana / CP per banana * 100%

Profit per banana = ₹ 3.00 - ₹ 2.50 = ₹ 0.50

Profit percentage = (0.50 / 2.50) * 100% = 20%

Therefore, the fruit seller made a profit of 20%.