To find the unit rate of minutes per mile, you need to divide the total minutes by the total miles. Oscar runs a total of 7 miles in 84 minutes.
So, the calculation is:
\[ \text{Unit Rate} = \frac{\text{Total Minutes}}{\text{Total Miles}} = \frac{84 \text{ minutes}}{7 \text{ miles}} = 12 \text{ minutes per mile} \]
Thus, the unit rate is 12 minutes per mile.