Question 1126156
<pre>
                   SPEED     TIME     DISTANCE
upstream          25-7=18    2/18         2        
downstream        25+7=32    2/32         2      
</pre>


Total Distance, 4 kilometers
Total Time, {{{1/9+1/16=25/(9*16)}}}


Average round trip speed, 

{{{(4*9*16)/25=23.04}}}

About 23 kilometers per hour