A company discovers that to produce x
=
700 new electronic parts, it will cost
y
=
$62400. To produce 520 new electronic parts, it will cost $46920.

Compute the slope of the costs and choose the most accurate statement from the following:
Costs are increasing at a rate of $86 per item.
Costs are increasing at a rate of $84 per item.
Costs are increasing at a rate of $81 per item.
Costs are decreasing at a rate of $81 per item.
Costs are decreasing at a rate of $86 per item.
Costs are decreasing at a rate of $84 per item.