How much interest rate would make his earnings the same
I don't know how you got 48% (and it would have been appropriate to include your work in your question), but think about it intuitively. Take your second to last step. If the landowner lends to the villagers and on average gets 60 dollars plus interest back, then if the interest rate was 80%, you'd get 60 + 48 = 108 dollars, the same as depositing to the commercial bank.

Algebraically, here's how you'd set up solving for $r$:

$$(100 \cdot (1+r))0.6 + 0(0.4) = 108$$

Where you have a 60% chance of being paid back 100 with interest. Then you just solve.