o = number of oat cereal, w = number of wheat cereal, f = number of fruit cereal:
o + w + f = 4250
o = w + 715
f = 5w
The second equation tells us the value of o in terms of w, and the third equation tells us the value of f in terms of w, so we can plug in "w + 715" for o and "5w" for f in the first equation:
o + w + f = 4250
(w + 715) + w + (5w) = 4250
Then, add like terms and subtract and divide to isolate the w:
w + 715 + w + 5w = 4250
7w + 715 = 4250 Subtract 715 on both sides:
7w = 3535 Divide by 7 on each side:
w = 505
Now that we have w, we can plug it into the last equation to find f, the number of fruit cereal boxes:
f = 5w
f = 5(505)
f = 2525
Therefore, the factory packages 2525 fruit cereal boxes.