How many pounds of screws costing $8 per pound must be mixed with 6 pounds of screws costing $3 per pound to yield a mixture costing $5 per pound?

Let x represent the number of pounds of screws costing $8 per pound.
1. The total cost of the mixture is the sum of the cost for each type of screw, or M=A+B, where:
A=8x is the cost for the $8-per-pound screws,
B=3×6=18 is the cost for the $3-per-pound screws,
M=5(6+x) is the total cost of the mixture.
2. Substitute these values into the equation:
5(6+x)=8x+18
3. Solve for x:
30+5x=8x+18
30−18=8x−5x
12=3x
x=4