Find the variation constant, and an equation of variation for each prob- lem below: (i) y varies directly as x, and y = 30 when x = 5. (ii) y varies directly as x, and y = 2 when x = 5. (iii) y varies inversely as x, and y = 5 when x = 20. (iv) y varies inversely as x, and y = 27 when x = 7. (v) y varies jointly as x and z, and y = 48 when x = 2, z = 4. (vi) y varies directly as a and z, and inversely as the cube of w, and y = 125 when x = 10, z = 20, w = 2.