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4. A spherical hailstone grows in a cloud. The hailstone maintains a spherical shape while its radius increases at a rate of 0.2 mm/min a. Express the radius, r, in millimetres, of the hailstone, as a function of the time, t, in minutes b. Express the volume, V, in cubic millimetres, of the hailstone, in terms of r c. Determine (Vr)(t) and explain what it means. d. What is the volume of the hailstone 1h after it begins to form