Hi I need help figuring out this problem in excel.

An explosion at a construction site could have occurred as the result of static electricity, malfunctioning of equipment, carelessness or sabotage. Interviews with construction engineers analyzing the risks involved led to the estimates that such an explosion would occur with probability of 0.25 as a result of static electricity, 0.20 as a result of malfunctioning of equipment, 0.40 as a result of carelessness, and 0.75 as a result of sabotage. It is also felt that the prior possibilities of the fours cause of the explosion are 0.20, 0.40, 0.25 and 0.15. Based on all this this information, what is:

• The most likely cause of explosion?
• The least likely cause of explosion?

Hint: in setting up your initial tree, remember that the first set of probabilities that are for the explosion given static electricity, malfunction, carelessness or sabotage. The second set of probabilities are for each of those types of situations to occur.