please answer it!

A 5 ft tall man is walking away from a 25 ft tall lamp post. If he is walking at a rate of 3 ft/s, at what rate is the length of his shadow changing? Note: Write only the numerical value of the rate, the units are already written. Write the exact answer not the decimal approximation (for example write - not 0.5) Answer. The length of his shadow is Click for List at a rate of