Answer:
7 mph
Step-by-step explanation:
Let x be the speed in still water hence
Time to move downstream will be [tex]\frac {66}{x+4}[/tex]
Time to move upstream will be [tex]\frac {66}{x-4}[/tex]
Difference will be
[tex]\frac {66}{x-4}-\frac {66}{x+4}=16[/tex]
[tex]66(x+4)-66(x-4)= 16(x^{2}-16)[/tex]
[tex]66x+264-66x+264=16x^{2}-256[/tex]
[tex]16x^{2}-256-528=0[/tex]
[tex]x^{2}-16-33=0[/tex]
[tex]x^{2}=49[/tex]
x=7
