To find the unit cost, you need to determine the cost per hour since the given time is half an hour.
- The cost for half an hour is $1.75.
- To find the cost for a full hour, you can double the half-hour cost: \[ \text{Cost per hour} = 2 \times 1.75 = 3.50 \]
Therefore, the unit cost is $3.50 per hour.