Answer:
56 hours 25 minutes
Step-by-step explanation:
Given:
Suppose it takes 45 hours for robot A to construct a new robot
It takes 25 hours for both robots to construct a new robot.
Question asked:
How long would it take robot B to construct a new robot, working alone ?
Solution:
Let the time taken by robot B to construct new robot = 
<u>By robot A</u>
It takes 45 hours to construct = 1 new robot
It takes 1 hour to construct = 
<u>By robot B</u>
It takes
hours to construct = 1 new robot
It takes 1 hour to construct =
new robot
<u>By working together</u>
It takes 25 hours to construct = 1 new robot
It takes 1 hour to construct = 
new robot is constructed in = 1 hour
<u><em>New robot is constructed by both working together in 1 hour = New robot is constructed by robot A in 1 hour + New robot is constructed by robot B in 1 hour </em></u>

Subtracting both sides by 


Thus, robot B would take 56 hours 25 minutes to construct a new robot, working alone.