Answer:
The minimum unit cost is $9374.
Step-by-step explanation:
The unit cost <em>C</em> for making <em>x</em> engines is given by the quadratic function:

We want to determine the minimum unit cost.
Since this is a quadratic function with a positive leading coefficient, the minimum value will be its vertex. The vertex of a quadratic can be found using the following formulas:

In this case, <em>a</em> = 0.3, <em>b</em> = -162, and <em>c</em> = 31244.
Find the <em>x-</em>coordinate of the vertex:

In other words, in order to achieve the minimum cost, only 270 engines must be made.
Then to find the minimum cost, substitute the value back into the function. So:

The minimum unit cost is $9374.