Answer:
It is said in Networking that a Hub is a dumb device means that it does not perform any look up while forwarding the data frame but broadcasts it indiscriminately which cause flooding. So in the given Question there are 7 devices which are connected to the Hub . When any one of them sends data frame to another one, the Hub broadcasts this data to all the machines connected to Hub. So the number of devices that see a particular message including sender is 7 and that is the answer.