Hello there!
Your answer would be 1.71%
Here is the work:
To find the annual paid interest for Farmer's Bank, since in the question it is the quarterly interest rate:
(1+(0.05/4))^4 -1 = 1.0125^4 -1 = 0.0509 = 5.09%
Merchant's bank would be the same rate since it's already calculated as annually: 6.8%
Subtract those:
6.8-5.09 = 1.71%