Mutual inductance

Derive the expression for mutual inductance induced in a trapezoidal structures having height h, side thickness s and base width b. a coil is wound in the trapezoidal structure with N1 turns. A circular coil of X turns carrying current of I ampere at frequency f. Two trapezoidal structures(turns N1 each) are placed on the sides in the opposite way. That is one trapezoidal structure in straight way and other in inverted way and oppositely placed. A circular ring carrying current produces mutual inductance on the trapezoidal structures. I need an generalized expression for mutual inductance induced on the trapezoidal structure wound with coils.