Task: Question Answering
Input (English): Problem: an engine moves at the speed of 90 kmph without any coaches attached to it . speed of the train reduces at the rate that varies directly as the square root of the number of coaches attached . when 4 coaches are attached speed decreases to 78 kmph . what will be the speed of train when 16 coaches are attached . 
Options: a ) 66 , b ) 72 , c ) 80 , d ) 68 , e ) 73
Output (English): a