How many pounds of coffee beans selling for $ 1.20 per pound should be mixed
with 6 pounds of coffee beans selling for $2.00 per pound to obtain a misture
selling for $1.68 per pound?

Let x = the number of pounds that must be mixed

Then 6+x = the number of pounds after mixing them

 MONEY HE          MONEY HE         MONEY HE 
WOULD TAKE        WOULD TAKE       WILL TAKE
 IN IF HE          IN IF HE        IN WHEN HE
 SOLD THE          SOLD THE         SELLS THE
 6 POUNDS     +    x POUNDS    =   6+x POUNDS   
 AT $2.00          AT $1.20         AT $1.60
 PER POUND         PER POUND        PER POUND
  WITHOUT           WITHOUT           AFTER
  MIXING            MIXING            MIXING
     ¯                 ¯                ¯
  2.00(6)      +     1.20x     =    1.60(6+x)
    
Can you solve that?  Answer: x = 6  

[It just happened to turn out to require equal amounts of each! 
That doesn't usually happen, but it did this time.]

Edwin
AnlytcPhil@aol.com