A15-ft ladder leaning against a wall begins to slide. How fast is the top of the ladder sliding down the wall at the instant of time when the bottom of the ladder is9ftfrom the wall and sliding away from the wall at the rate of4ft/sec?

Hint:Refer to the accompanying figure. By the Pythagorean Theorem,x²+y²=225.

Finddy/dt

whenx=9

anddx/dt=4.

(Round your answer to two decimal places.)