To allow the plane to land. A plane could use pontoons as well as or instead on wheels to land on water. As a general rule though, all of then have wheels, as it would be impractical to only be able to land on water.
It has four
Wheels and cockpit are two parts of a plane with propellers.
NO it does not have motors
They are know as the undercarriage.
They have 3 wheels, 2 rear and 1 front.
The wheels allow the plane to move around while it is on the ground.
To get wheels
It depends on the size of the plane. Some small planes have only 3 wheels. Some big planes have 10 or more wheels. It depends on the plane. A Piper or Cessna commuter plane is going to have a lot less wheels than does a B-52, 747 or C-5 Galaxy.
If a plane didn't have landing gear(the wheels and the "legs") it would have to land sliding on its belly. It would be fairly uncomfortable, damage the plane, and on top it would be very hard to reach take off speeds like that.
The purpose is to transmit power from the transmission to the wheels
No they are not. An inclined plane is a flat surface which has a slope to it i.e. it is flat but not level.
To keep you rolling smoothly.