we have
[tex]d=4 -\frac{1}{15}t[/tex]
using a graph tool
see the attached figure
For t=0 d=4 -------> the y-intercept
that means that at the time t=0 the house was four units away.
For t=60 min d=0 -------> x-intercept
that means he was already at home at the time t=60 minutes.
therefore
the graph of this equation represents the walk towards the house