River shore is located at distance
[tex]d = 4 km[/tex]
speed of the woman is given as
[tex]v_1 = 2.5 m/s[/tex]
now the time taken by the woman to cover the distance is
[tex]t = \frac{d}{v}[/tex]
[tex]t = \frac{4000}{2.5} = 1600 s[/tex]
for the same time interval the dog will run to and fro with speed 4.5 m/s
so the total distance moved by the dog is given by
[tex]d = v* t[/tex]
[tex]d = 4.5 * 1600 [/tex]
[tex]d = 7200 m[/tex]
so the total distance that dog will move is 7200 m or 7.2 km