Explanation:
Let's let
represent the cost of tapes, and
be the cost of CDs.
From the problem statement, we can create the following two equations:


To solve this system of equations, we can solve for
in the second equation and substitute into the first equation to get the value of
:


Substitution:




Now that we know the cost of the tapes, we can plug this value into either equation to get the cost of CDs:





or




Therefore, the cost of a tape is
and the cost of a CD is
.