marking up prices formula

I have found some threads on how to mark up prices using a percentage in excel, but I have not found out how I can put a percentage in one cell and have all the prices update. With the formulas I found, I have to go through every cell and input the formula to have it the prices updated. Any help would be very much appreciated. The formulas I have found are "=A1+(A1*B1)" and "=COST/(1-MARKUP)". These work but I have to type this in every cell to update the price. I am including my spreedsheet that I am working on to give you an idea of what I need.