I don't understand how to do related rates?

Question

A ladder 10 meters long rests on horizontal ground and leans against a vertical wall. The foot of the ladder is pulled away from the wall at the rate of 0.5 m/sec. How fast is the top sliding down the wall when the foot of the ladder is 6 m from the wall?

Answer 1

tan(theta)  =8/6 = 4/3 Where theta is the angle with horizontal when x = 6m = y/x(as y= 8m when x= 6 m)

y=4/3(x)

 

 

dy/dt =( 4/3) dx/dt

 Speed on wall =( 4/3 ) speed on ground = (4/3) 0.5 =2/3 m/s = Speed on the wall