Answer:
Let [tex]x[/tex] be the speed of the river current, [tex]t_{1}[/tex] be the speed upstream and [tex]t_{2}[/tex] be the speed downstream.
[tex]t_{1} =2t_{2}[/tex]
[tex]\frac{60}{x-3} =2(\frac{60}{x+3} )[/tex]
[tex]x+3=2(x-3)[/tex]
[tex]2x-x=3+6[/tex]
[tex]x=9[/tex]
Therefore the speed of the river current is 9mph.