A store sells cashews for $6.00 per pound and peanuts for $3.00 per pound. The manager decides to mix 20 pounds of peanuts with some cashews and sell the mixture for $4.00 per pound. How many pounds of cashews should be mixed with the peanuts so that the mixture will produce the same revenue as would selling the nuts separately? There should be pounds of cashews in the mixture. (Type an integer or a decimal.)