Task: Question Answering
Input (English): Problem: one robot builds a robot in 1 hour , another one builds a robot in 2 hours . the 2 robots work together and when a new robot is complete , it joins the others , working at a constant rate of one robot in 2 hours . how much time will it take until there are 4 robots altogether , if the robots build only one robot at a time ? 
Options: a ) 70 min , b ) 94 min , c ) 110 min , d ) 112 min , e ) 120 min
Output (English): a