Answered

The cost of mailing a DVD in an envelope by express mail is equal to the cost of mailing a DVD in a box by priority mail. What is the weight of the DVD with its packing material? Round your answer to the nearest hundredth. 
                Packing  Material           Priority Mail               Express Mail 
Box=             $2.25                     $2.50 per lb                   $8.50 per lb 
Envelope=    $1.10                        2.50    per lb              $8.50 per lb



Answer :

eight of the DVD with packing material is 0.19 lb. 
1.10+8.5x=2.25+2.5x
Move variables to one side. The easier one would be to move 2.5x. So you subtract 2.5x to both sides.
1.10+6x=2.25
Do the same for the values without the x. The easier one would be to subtract 1.10 from both sides. 
6x=1.15
Then divide by 6
1.15/6=0.19