A toroidal solenoid has an inner radius of 12.0 cm and an outer radius of 15.0 cm . It carries a current of 1.50 A . Part A How many equally spaced turns must it have so that it will produce a magnetic field of 3.75 mT at points within the coils 14.0 cm from its center? Enter your answer numerically. mastering physics

The number of turns is  

Explanation:

From the question we are told that

  The inner radius is

   The outer radius is  

   The current it carries is

    The magnetic field is  

   The distance from the center is

Generally the number of turns is mathematically represented as

Generally   is the permeability of free space with value  

So

15.3 cos 65 degrees trig

i think the answer would be b