well, let's split the hours in minutes, so since 1 hr is 60 minutes, so he can walk 2.833 miles in 60 minutes, well, 3 hrs is 3*60 = 180 minutes, then we add 15 minutes, that's 195 minutes.
if he can walk 2.833 miles in 60 minutes, how long will it be for 195 minutes?
[tex]\bf \begin{array}{ccll} miles&minutes\\ \cline{1-2} 2.833&60\\ x&195 \end{array}\implies \cfrac{2.833}{x}=\cfrac{60}{195}\implies \cfrac{2.833}{x}=\cfrac{4}{13} \\\\\\ 36.829=4x\implies \cfrac{36.829}{4}=x\implies 9.20725 = x[/tex]
