Task: Question Answering
Input (English): Problem: on a trip covering 450 km , a bicyclist travels the first 300 km at 20 km per hour and the remainder of the distance at 15 km per hour . what is the average speed , in km per hour , for the entire trip ? 
Options: a ) 16.5 , b ) 17.0 , c ) 17.5 , d ) 18.0 , e ) 18.5
Output (English): d