Any unamortized premium should be reported on the balance sheet of the issuing corporation as

It should be an addition to the face amount of the bonds in the liability section. This is because a premium on a bond investment made is usually recorded in the account for investment and amortized over it’s known useful life

an addition to the face amount of the bonds in the liability section

Explanation:

When a bond is sold at a premium, it means that its market price was higher than its face value, e.g. face value = $100, market value = $105 results in a $5 premium.

the journal entry for this example should be:

Dr Cash 105

    Cr Bonds payable 100

    Cr Premium on bonds payable 5

Both bonds payable and premium on bonds payable are liability accounts.  

answer; i believe the correct answer is (a) purchase of treasury stock;