To determine the rate at which the oil spill is spreading, we can start by calculating the area covered by the spill in terms of square kilometers per hour.
- The area covered by the oil spill: 4 square kilometers.
- Time taken to cover this area: \( \frac{1}{4} \) hour.
Now, we can calculate the rate of spread in square kilometers per hour:
\[ \text{Rate of spread} = \frac{\text{Area}}{\text{Time}} = \frac{4 \text{ km}^2}{\frac{1}{4} \text{ hour}} = 4 \text{ km}^2 \times 4 \text{ hours}^{-1} = 16 \text{ km}^2/\text{hour} \]
So, the oil spill is spreading at a rate of 16 square kilometers per hour.