We take the formula µ = g*µ_N*I.
a) We have spin 1/2 and µ = -0.5940µ_N, putting this in the formula above, we find that g = -1.188. For the 245 keV level, we have spin 5/2 and µ = -0.766µ_N, working this out, we find g = -0.3064.
b) Using the same fomula as above, with µ_N replaced by µ_B and using that the electron has spin 1/2, we find that g = 2.
c) Again using the formula above with spin 1/2 and g = -3.826, we find that µ = -1.913.