Please refer to the attached file. It begins:
A magnetic core with its dimensions is shown in the attached figure...
For leg c,
N = 100 turns
I = ?
phi = 6.5 mWb = 6.5*10^(-3) Wb
A = 10*5 cm^2 ...
The solution explains where each calculation it uses to answer this question on the magnetic core described by the asker and then does them in a clear order to find the current required to produce a certain flux.