Costing

In marginal costing chp we have one sum wer we need to find out profit by way of absorption costing method n marginal costing method n reconcile it. In absorption costing..in case of fixed overheads..dat under/(over) absorption effects should it be given directly to fixed overheads (supplementary rate method) or to cost of sales? And if both methods are appropriate which one to follow wen? bcoz by both d methods profit will differ.