Let x represent the rate Ina can row in still water and 
let y represent the rate of the current. 


Then  her  effective speed downstream  is  x+y   miles per hour,
while her  effective speed upstream    is  x-y  miles per hour.


    // It is first major point you need understand and use in this sort of problems.


Now, "speed" equation for boat floating downstream is 

 = u + v    (1)    (speed downstream = the distance divided by time downstream)


Next, "speed" equation for boat floating upstream is 

 = u - v    (2)    (speed upstream = the distance divided by time  duptream)


    // It is the second major point in solving such problems: you must understand and write these equation automatically !


Simplify equations (1) and (2)


u + v =  8     (3)
u - v =  3     (4)


Now add equations (3) and (4) to eliminate "v". You will get


2u = 8 + 3 = 13  ====>  u =  = 6.5.


Thus you just found the boat' speed in still water. It is 6.5 miles per hour.


Next, you can find the current rate from eq(4)  v = 8 - u = 8 - 6.5 = 1.5 miles per hour.


Answer.  The boat' speed in still water is 6.5 miles per hour.

         The current speed is 1.5 miles per hour.



Solved.  I advise you to make the check on your own.


         After making the check, you will understand the problem and the solution MUCH better.