Related Rates - Car Driving Past a House

HELP

     
One mile from a house, down a straight road, is an intersection. A highway runs through the intersection, perpendicular to the road to the house. Suppose an automobile travels 60 mph along the highway
  1. How fast is the distance between the car and the house increasing when the car is `3` miles past the intersection?
  2. How fast is the distance between the car and the house increasing when the car is `x` miles past the intersection?
  3. Confirm your answer to the previous part by substituting `x = 3` and `x = 0`.
  4. Suppose the speed of the car `x` miles past the intersection is a function `s(x)`. (So previously, `s(x) = 60` was a constant function.) Now how fast is the distance between the car and the house increasing when the car is `x` miles past the intersection?