Question 99931
12x+9(20-x)=10*20
12x+180-9x=200
3x=200-180
3x=20
x=20/3 pounds of $12 coffee is needed.
20-6 2/3=13 1/3 or 40/3 pounds of $9 coffee is needed.
proof
12*20/3+9*40/3=200 
240/3+360/3=200
80+120=200
200=200