To find the unit cost, you divide the total cost by the total weight.
The total cost for 4 pounds of bananas is $3.16.
To find the cost per pound, you calculate:
\[ \text{Unit cost} = \frac{\text{Total cost}}{\text{Total weight}} = \frac{3.16}{4} \]
Calculating this gives:
\[ \text{Unit cost} = 0.79 \]
So, the unit cost is $0.79 per pound.