please solve the question mathematically

1. A skydiver with a weight of 80kg descends through air with his head down. If the area of the skydiver is approximately 0.2m2 and a drag coefficient of approximately 0.5. Consider the temperature of the air as 250K. a) What is his terminal velocity? b) Find the expression for the thickness of boundary layer around his body. Solve this part when i) there is no pressure gradient and ii) there exists pressure gradient around the body