A launch rocket for a space exploration vehicle has a sensing system that can stop the launch if the pressure in the fuel manifold falls below a critical level. The system consists of four pressure switches ( for = 1,2,3,4), which should open (preventing current flow) if the pressure falls below the critical level. They are linked into an electrical connection between terminals and as shown in the diagram. If current cannot flow from to the launch is stopped. Assume that each switch fails to open when it should with probability and that failures of switches are independent. Find the probability that the launch will not be stopped if the pressure drops below the critical level in terms of