HELP PLEASE!! DUE IN 10 MINUTES

Amerchant has coffee worth $60 a pound that she wishes to mix with 50 pounds of coffee worth $90 a pound to get a mixture that she will sell for $70 a pound. how many pounds of the & 60 coffee should be used?

What’s the answer ? use the picture to see the problem

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.