Task: Question Answering
Input (English): Problem: a boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream . if the speed of the boat in still water is 10 mph , the speed of the stream is : 
Options: a ) 4 mph , b ) 2.5 mph , c ) 3 mph , d ) 2 mph , e ) none of these
Output (English): d