I want have an explanation for this case. dor the tree diagram formula for bidding

The decision tree diagram shows the choice between two contracts for which a business can bid. The cost of Contract 1 is $10 million. The cost of Contract 2 is $18 million. The net gain of Contract 1 is $4 million. (0.6) $20 million $10 million Success Contract 1 Failure $5 million (0.4) (0.8) $25 million $18 million Success Contract 2 Failure $4 million (0.2) Calculate the net gain of Contract 2. Show your working