Question

Small boxes contain DVDs, and large boxes contain one gaming machine. Three boxes of gaming machines and a box of DVDs weight 48 pounds. Three boxes of gaming machines and five boxes of DVDs weight 72 pounds. How much does each box weigh?

Answer 1

3g + d = 48....multiply by -1
3g + 5d = 72
-----------------
-3g - d = -48 (result of multiplying by -1)
3g + 5d = 72
----------------add
4d = 24
d = 24/4
d = 6 <==== DVD boxes weigh 6 lbs

3g + d = 48
3g + 6 = 48
3g = 48 - 6
3g = 42
g = 42/3
g = 14 <=== gaming boxes weigh 14 lbs