Task: Question Answering
Input (English): Problem: a river boat leaves silver town and travels upstream to gold town at an average speed of 4 kilometers per hour . it returns by the same route at an average speed of 7 kilometers per hour . what is the average speed for the round - trip in kilometers per hour ? 
Options: a ) 5.1 , b ) 7.1 , c ) 7.2 , d ) 7.5 , e ) 8.0
Output (English): a