On part (b), there is an equation which (332,600-320,000)/63*4=800. Why they do *4? How to find 4?

On April 1, 2012, West Co. purchased $320,000 of 6% bonds for $332,600 plus accrued interest as an available-for-sale security. Interest is paid on July 1 and January 1 and the bonds mature on July 1, 2017. (a) Prepare the journal entry on April 1, 2012. (b) The bonds are sold on November 1, 2013 at 103 plus accrued interest. Amortization was recorded when interest was received by the straight-line method (by months and round to the nearest dollar). Prepare all entries required to properly record the sale