Macro to calculate discount

hi
I have a table in sheet1 and it has four colomns named product, price, discount volume and discount(in percentage %).


Now i have one another table in sheet1 also under the last table and i want that when i enter the volume then it check that whether it is more or less than Discount volume(in table 1). if it is more then calculate with given discount else only multiply price with volume.

i have given excel file here....


please help me.....