If a person rows to this favorite fishing spot 17 miles downstream in the same amount of the time he rows 1 mile upstream and if the current is 8mph, find how long it takes him to cover 18 miles

We use the formula : Displacement = Average Velocity * Time ;
17 = ( v + 8 ) * t ;
1 =  ( v - 8 ) * t ;
where v = the velocity of the boat; t is the time from expression " ... in the same amount of the time he rows "

Then 17 / 1 = (v + 8) / ( v - 8 ) ;
v + 8 = 17( v - 8 );
v + 8  = 17v - 136 ;
144 = 16v ;
v = 144 / 16;
v = 9 mph ;

18 = 9 * x ;
x = 18 / 9 ;
x = 2 hours ;

The answer is 2 hours ;