At what rate is the tip of her shadow moving away from the light (ie. away from the top of the pole) when the girl is 50 ft away from the pole?

Question

A street light is at the top of a 28 ft pole. A 4 ft tall girl walks along a straight path away from the pole with a speed of 5 ft/sec. 

Answer 1

Let y is coordinate of girl and x is length of shadow. Then 28/4 = (y + x)/x; 7x = y + x; 6x = y, x = y/6

dx/dt = (dy/dt)/6 = 5/6 ft/sec