The relationship between the total cost and the costs of CDs and DVDs are represented by a linear function.
The cost of DVD is $15
Let:
[tex]D \to DVD[/tex]
[tex]C \to CD[/tex]
The cost of both is represented as:
[tex]C + D = x[/tex]
Where
[tex]C = x - 15[/tex]
Substitute [tex]C = x - 15[/tex] in [tex]C + D = x[/tex]
[tex]D = x - C[/tex]
[tex]D = x - [x - 15][/tex]
Open bracket
[tex]D = x - x + 15[/tex]
[tex]D = 15\\[/tex]
Hence, the cost of DVD is $15
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