#### Answer

The average velocity of the boat in still water is $6$ km/h and that of the current is $2$ km/h.

#### Work Step by Step

Step 1. Assume the average velocity of the boat in still water is $x$ km/h and that of the current is $y$ km/h.
Step 2. When traveling with the stream, the total average velocity is $x+y$; thus $2(x+y)=16$ or $x+y=8$
Step 3. When traveling against the stream, the resulting average velocity is $x-y$; thus $4(x-y)=16$ or $x-y=4$
Step 4. Adding the two equations, we get $2x=12$; thus $x=6$ and $y=2$.