The Base of a 35-Foot Ladder Is Being Pulled Away $9 \frac { \mathrm { ft } } { \mathrm { s } }$

Multiple Choice

The base of a 35-foot ladder is being pulled away from a wall at a rate of 12 feet per second. How fast is the top of the ladder sliding down the wall at the instance when the base of the ladder is 21 feet from the wall ?

A) $9 \frac { \mathrm { ft } } { \mathrm { s } }$
B) $48 \frac { \mathrm { ft } } { \mathrm { s } }$
C) $36 \frac { \mathrm { ft } } { \mathrm { s } }$
D) $16 \frac { \mathrm { ft } } { \mathrm { s } }$
E) $3 \frac { \mathrm { ft } } { \mathrm { s } }$