Shelly-Ann normally runs along the Laurel Trail at a constant speed of $8 \mathrm{~m} / \mathrm{s}$. One day, onethird of the trail is covered in mud, through which Shelly-Ann can only run one-quarter of her normal speed, and it takes her 12 s to run the entire length of the trail. How long is the trail, in metres?
Suppose that the length of the trail is $d \mathrm{~m}$.

On the muddy day, Shelly-Ann runs $\frac{1}{3} d \mathrm{~m}$ at $2 \mathrm{~m} / \mathrm{s}$ and $\frac{2}{3} d \mathrm{~m}$ at $8 \mathrm{~m} / \mathrm{s}$.

Since this takes 12 seconds in total, then $\frac{\frac{1}{3} d}{2}+\frac{\frac{2}{3} d}{8}=12$.

Multiplying both sides by 8 , we obtain $\frac{4}{3} d+\frac{2}{3} d=96$ which gives $2 d=96$ or $d=48$.

Therefore, the trail is 48 metres long.

ANSWER: 48 metres