Final answer:
The unit rate that the water is evaporating at is 5/36 inch per hour.
Step-by-step explanation:
To find the unit rate that the water is evaporating at, we need to divide the amount of water evaporated by the time it takes to evaporate.
The rate of evaporation is 5/8 inch every 4 1/2 hours.
To divide a fraction, we invert the second fraction and multiply. So, the unit rate is (5/8) / (9/2) = (5/8) * (2/9) = 10/72 = 5/36 inch per hour.
Therefore, the correct unit rate is 5/36 inch per hour.