4. A training aircraft is used to train astronauts. The equation that models its flights is given by h = -10t + 300t + 9750 where h is the altitude in metres and t is the time in seconds. The graph is shown right. Height (m) Time (s) a). What is the initial height of the aircraft? /1 b). What is maximum height of the aircraft and when does it reach the 12 maximum height? c). How long is the aircraft in the air? /1 d). The astronauts will be weightless when the aircraft is above 11 000 m. How long will the astronauts experience weightlessness