X varies directly as √Y. When Y = 20.25, X = 18. What is the value of Y when X = 7.2?

X varies inversely as Y and Y varies inversely as Z. In a particular case, X = 14 and Z = 1140. What will be the value of X, when Z = 16?

The force needed to keep a car from skidding on a curve varies directly with the weight of the car and the square of its speed, and inversely with the radius of the curve. Suppose 7,160 pound-force is required to keep a 2,864-pound car traveling at 30 mph from skidding on a curve of 120 feet. How much pound-force is required to keep a 3,000-pound car traveling at 40 mph from skidding on a curve of 400 feet?