I want to set up my spreadsheet to calculate the product (column K) by multiplying the price of an item (column I) by the quantity purchased (column J).

i.e. every price point in column 'I' to be multiplied by every quantity in column 'J' and the total to be given in column 'K'

or

I*J=K 5.99 * 1 = 5.99 1.99 * 2 = 3.98 etc