At the old price of $6.00 per pound, that would cost $21.00. If the cheese price is marked up 15%, then it will cost 6 x1.15=$6.90/ pound. So the new cost would be $6.90 x 3.5 = $24.15. So in other words, it would now cost $3.15 more in total for the 3.5 pounds.
