C is partly constant and partly varies as d. When d = 2, C = 10. When d = 5, C = 19. Find C when d = 8.
The cost $C of running a machine is partly constant and partly varies as the hours h used. For 3 hours, C = $45. For 7 hours, C = $85. Find the formula and C for 10 hours.
y is partly constant and partly varies as x2. When x = 2, y = 14. When x = 4, y = 38. Find y when x = 3.