In an assembly line of a factory, which produces networking switching hubs, two robots are utilized. The first one (A) is able to produce 40 microchips per hour, whereas the second one (B) produces 30 microchips per hour. For a total production of 400 microchips, the two robots operated for 12 hours. How many hours did each robot work?

Question

In an assembly line of a factory, which produces networking switching hubs, two robots are utilized. The first one (A) is able to produce 40 microchips per hour, whereas the second one (B) produces 30 microchips per hour. For a total production of 400 microchips, the two robots operated for 12 hours. How many hours did each robot work?
(1) clearly define your variables: state what they represent and what their relations are in terms of the information given in the problem statement, 
(2) setup your equations, 
(3) solve the system, 
(4) check/validate your solutions and 
(5) summarize your findings in a sentence that refers to what the problem asked.