Corporate Finance, I need help to answer question b and c (calculating NPV of outcomes in decision tree).

Magna Charter is a new corporation formed by Agnes Magna to provide an executive flying service for the southeastern United States. The founder thinks there will be a ready demand; however the venture is not a sure thing. There is a 40% chance that demand in the first year will be low.If it is low, there is a 60% chance that it will remain low in subsequent years. On the other hand, if the initial demand is high, there is an 80% chance that it will stay high.

The immediate problem is to decide what kind of plane to buy. A turboprop costs $350,000. A piston-engine plane costs only $180,000 but has less capacity and customer appeal. Moreover, the piston-engine plane is an old design and likely to depreciate rapidly. Ms. Magna thinks that next year second-hand piston aircraft will be available for only $150,000. That gives Ms. Magna an idea: why not start out with one piston-engine plane and buy another one if demand is still high? If the demand is low, Magna Charter can sit tight with one small, relatively inexpensive aircraft.

The following graph displays these choices: