barbara just finishned putting together the performance report for her division using stan ard costs within a variable costing system . operating income is $1600 for this period when there was a decrese in FG inventory of 660 units barbara reported fixed MOH costs of $13920 she is happy to find there are no variable cost variances this period and actuaql production equaled budgeted production of 4640 units last periods inventory carried the same cost per unit as