Task: Question Answering
Input (English): Problem: a certain number of horses and an equal number of men are going somewhere . half of the owners are on their horses ' back while the remaining ones are walking along leading their horses . if the number of legs walking on the ground is 90 , how many horses are there ? 
Options: a ) 10 , b ) 12 , c ) 14 , d ) 16 , e ) 18
Output (English): e