He takes 2 hours to walk 3 miles.
If d is the distance and t is the time, and we are assuming a constant proportionality relationship between these two variables, we have:
[tex]d=k\cdot t[/tex]We can calculate k (in this case is the average speed) knowing that he takes 2 hours (t=2) to cover 3 miles (d=3). As this point (2,3) belongs to the line, we replace and calcualte:
[tex]\begin{gathered} d=k\cdot t \\ 3=k\cdot2 \\ k=\frac{3}{2} \end{gathered}[/tex]Then, we can write the relationship between distance d and time t as:
[tex]d=\frac{3}{2}\cdot t[/tex]