If they instead chose front and back covers of thickness 1/3 of an inch, how would this change the equations in the previous two parts

Two blends of tea are mixed to make a blend that will be sold at the fair. black tea sells for $2.20 per pound and orange pekoe tea sells for $3.00 per pound. how much of each should be used to obtain a 4lb blend selling for $2.50 per pound?

Can someone check if i did this correct. it’s number 4 if you’re wondering.

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?