Question

A person wishes to mix coffee worth ​$9 per lb with coffee worth $3 per lb to get 180lb of a mixture worth ​$5 per lb. How many pounds of the ​$9 and the ​$3 coffees will be​ needed?

Answer 1

60lb of $9 worth coffee and
120lb of $3 worth coffee
note this answer is purely a trial and error based answer but the amount of money remains that is $5 worth of coffee multiplied by 180lb will give you $900.
answers of coffee in lbs will/may vary but value($900) will be constant