What is the direction of the magnetic field due to solenoid

What is the direction of the magnetic field due to solenoid A at the center of solenoid B? What is the direction of the magnetic field due to solenoid B at the center of solenoid A? What is the direction of the force acting on solenoid A?

Solution

Right hand thumb rule plays a crucial roel in determining the directions of magnetic fields and forces due to magnetic fileds.

18) towards RIGHT
19) towards LEFT
20) Net force on solenoid A is ZERO