V = 2/3 pi r³ h 200 = 2/3 pi r³ h 300 = pi r³ h h = 300/ (pi)(r³) So this is the relationship that I find between height and radius. This is where I'm lost. The pricing of the cynlindrical wall and the hemisphere :S If I can get the formula for this one, I think I can solve the problem/ For this one, I tried to form a relationship between the speed, time and fuel but end up confusing myself. Am I supposed to take it 1 step at a time or what? I never studied this kind of optimization problem before.