## College Algebra (10th Edition)

Let $x$ be the amount of $6$ pound coffee, then $100-x$ is the amount of $9$ pound coffee, then our equation is: $6x+(100-x)9=100\cdot6.9\\6x+900-9x=690\\-3x=-210\\x=70$ Thus we mix $70$ pounds of $6$ pound coffee and $30$ pounds of $9$ pound coffee.