They hiked 12 miles on the first day
Here, we want to get the number of miles hiked
From the question, we have it that 1/3 of the trail was hiked
Mathematically, we have this as one-third of 36 miles
We have this as;
[tex]\frac{1}{3}\times36\text{ = }\frac{36}{3}\text{ = 12 miles}[/tex]