I got this wrong and i'm don't know how

A 5.2 ft tall man is walking away from a 26 ft tall lamp post. If he is walking at a rate of 4 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 increasing at a rate of 22/41 FUs