Candy is selling at $6.00 per pound will be mixed with candy selling at $9.00 per pound. how many pounds of the more expensive candy are needed to produce a 15 pound mixture that sells for $7.00 per pound

Use a table

Cost*amount=value
add collumes and multiply rows

C  x  A =  V
6      y  =  6y
9    15-y= 9(15-y)
7    15    = 105

6y+9(15-y)=105
6y+135-9y=105
-3y+135=105
subtract 135
-3y=-30
divide -3
y=10

15-y=15-10=5

10 pounds of $6 mixture
5 pounds of $9 mixture

check
10*6=60
5*9=45
60+45=105
7*15=105
105=105
check

10 pounds $6
5 pounds $9