For material A whose original standard consumption is 800 units at $24 as well as its actual consumption is 640 units at $ 26.Similarly for material B whose original standard consumption is 400 units at $ 20 as well as its actual consumption is 520 units at $ 20.It is decided to revise the standard consumption of material A to 680 and that of material B to 40 units to improve the quality of the product.Calculate material mix variance using Original Standard Mix Ratio, Revised Standard Mix Ratio.