Candy selling at $6.00 per pound with be mixed with candy selling $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?

Answer:
Amount of more expensive candy = 5 pounds
Amount of less expensive candy = 10 pounds

Explanation:
Assume that the amount of the more expensive candy is x and that the amount of the less expensive one is y.
We are given that:
1- The amount to be produced is 15 pounds. This means that:
    x + y = 15
    This can be rewritten as:
    x = 15 - y ..........> equation I
2- The expensive one costs $9, the less expensive one costs $6 and the one to be produced will cost $7. This means that:
9x + 6y = 7(x+y) ............> equation II

Substitute with equation I in equation II and solve for y as follows:
9x + 6y = 7(x+y)
9(15-y) + 6y = 7(15-y+y)
135 - 9y + 6y = 105
135 - 105 = 9y - 6y
30 = 3y
y = 30/3
y = 10

Substitute with the y in equation I to get the x as follows:
x = 15-y
x = 15-10
x = 5

Based on the above calculations:
Amount of more expensive candy = x = 5 pounds
Amount of less expensive candy = y = 10 pounds

Hope this helps :)