Explanation:

In these kind of Questions,

The Price ratio and Quantity ratio will be in reverse proportion.

Price Ratio = 100:60 = 5:3

So Quantity Ratio = 3:5

Now we can buy 64 more.

So Difference between the quantities bought in both cases is 64.

=> 5x - 3x = 64

x = 32

Now we can buy 5x = 5*32 = 160 Bananas

Reduced Price per Banana = 40 Rs./160 = 0.25 Rs./Banana

Reduced Price of 1 dozen Bananas = 0.25*12 = 3 Rs.