A street light is fastened to the top of a 16.5-ft-high pole. If a 5.5-ft-tall woman walks away from the pole in a straight line over level ground at a rate of 5 ft/s, how fast is the length of her shadow changing when she is 12 ft away from the pole? Let L be the length of the woman's shadow and let x be the woman's distance from the pole. Write an equation that relates L and x.