A 25-foot-long ladder is leaning against a wall and sliding toward the floor. If the foot of the ladder is sliding away from the wall at a rate of 2 ft/sec, how fast is the top of the ladder sliding down the wall when the top of the ladder is 7 ft from the ground?

a) 1 ft/sec
b) 1.5 ft/sec
c) 2 ft/sec
d) 2.5 ft/sec