Subject: mathqa
Question: 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 8 robots altogether , if the robots build only one robot at a time ?
Option: 
A: 110 min
B: 94 min
C: 146 1 / 7 min
D: 131 1 / 7 min
Answer: C