The rate of change is given as
[tex]\text{rate}=\frac{48400-46680}{550-530}[/tex]
which gives
[tex]\begin{gathered} \text{rate}=\frac{1720}{20} \\ \text{rate}=86 \end{gathered}[/tex]
Since the result is positive, the answer is the costs are increasing at a rate of $86 per item
