Mutual Inductance in a solenoid

[matt72lsu]

Homework Statement

A long solenoid (black coil) with cross-sectional area A cm^2 and length L is wound with n1 turns of wire. A time-varying current i1 flows through this wire. A shorter coil (blue coil) with n2 turns of wire surrounds it. Use (uo)(m*kg/s^2*A^2)
1) Find the value M of the mutual inductance.

Note: The current in coil 1 is constantly changing. However, when using the hints it may help you to consider the instant at which the current in coil 1 is A.

I don't exactly know how to post the image

Homework Equations

I used the above equation

The Attempt at a Solution

I got M = P*n1*n2*A/L but it was wrong. Not sure where I went wrong. Any help would be appreciated

 

[matt72lsu]

if a pic is necessary, i can probably describe it