Coffee A normally costs $ 100 per lb. It is mixed with coffee B, which normally costs $ 70 per lb, to form a mixture that costs $ 88 per lb. If there are 10 lbs of the mix, how many pounds of coffee A is used in the mixture?

Actually I don't get this problem properly.

What I got so far,

Coffee A costs $ 100 per lb, coffee B costs $ 70 per lb. Their mixture in certain ratio costs $ 88 per lb. Then how I count the ratio from this?