Average cost update Return to supplier

Item is Make as well Buy -

For Item prior to RTV , Item Cost = 248          OnHand = 313

                                      PO Price = 230  RTV Quantity = 276    Recoverable tax = 0

                  After RTV,  Item Cost = 1115         OnHand = 37

I want to know, how Item cost derived to 1115 ?

As per Average cost formula , Item cost was expected to 329

Following is the formula used for calculation:-

{[(prior cost * prior costed quantity ) + (transaction_cost * transaction quantity )] +taxes } / [prior costed quantity + transaction qty]

    

Following   is the formula used for calculation:-

{[(prior cost * prior costed   quantity ) + (transaction_cost * transaction quantity )] +taxes } / [prior   costed quantity + transaction qty]