If Trey has completed \( \frac{1}{4} \) of the race and he has already run 1.2 miles, we can find the total distance of the race.
Let \( D \) be the total distance of the race. Since he has run \( \frac{1}{4} \) of the race, we can express this as:
\[ \frac{1}{4}D = 1.2 \text{ miles} \]
To find \( D \), we can multiply both sides of the equation by 4:
\[ D = 4 \times 1.2 = 4.8 \text{ miles} \]
Now that we have the total distance of the race, we can find out how much more he needs to run to complete the race. He has completed \( \frac{1}{4} \) of the race, so he has \( \frac{3}{4} \) of the race left to run.
The distance left to run is:
\[ \frac{3}{4}D = \frac{3}{4} \times 4.8 = 3.6 \text{ miles} \]
Thus, Trey must run 3.6 miles more to complete the race.