Answer:
Width of river = 0.25 mile
As length of river is not given , but it is given that  campsite is located 1 mile east upstream, So length of river = 1 mile
Speed of mine in river while going upstream = 3 miles per hour
Speed of current as going Upstream = 1 miles per hour
Now Reduced speed of mine = Speed of mine in river while going upstream - Speed of current as going Upstream 
                                               = 3 - 1
                                               = 2 miles per hour
1. There are two ways to reach campsite 
(a) either walk 1 mile from starting point in east direction and then swim 0.25 mile in North direction to reach campsite.
Or
(b) From the starting point Considering a right triangle having, base=1 mile and altitude = 0.25 mile, then finding the length of hypotenuse using formula =  
 
=
=√1.0625
=1.03078(approx)
⇒ you must walk a distance of 1 mile in the east direction and then swim 0.25 mile north direction to reach directly at campsite.[shown in the diagram]