A hardware store makes a mixed bag of 42 items using screws, bolts, and washers. The cost of screws are $3.00 each, bolts cost $2.00 each, and washers are $1.50 each. The mixture calls for four times as many screws than bolts. The total cost of the mixture is $102.00. How much of each item did the store use?

Answer 1

s+b+w = 42
3s + 2b + 1.5w = 102.00
s = 4b

now crank it out.

Answer 2

s + b + w = 42

s = 4b

3s + 2b + 1.5w = 102

substituting
... 5b + w = 42
... 14b + 1.5w = 102