Step-by-step explanation: Here, notice that the value that we
don't know is how many CDs are purchased.
Since CD's cost $8, we multiply 8 by our variable, which is x.
So we have 8 times x or 8x.
In addition, since there is a one time fee
of $15 to begin, we add 15 to 8x.
So we have 8x + 15.
