To find the number of machines that minimize the unit cost, we need to find the value of x that minimizes the function C(x). We can do this by finding the critical points of C(x) and determining which one corresponds to a minimum.
First, we take the derivative of C(x) with respect to x:
C'(x) = 1.2x - 372
Then, we set C'(x) equal to zero and solve for x:
1.2x - 372 = 0
1.2x = 372
x = 310
So the critical point is x = 310.
To determine whether this critical point corresponds to a minimum or a maximum, we need to examine the second derivative of C(x):
C''(x) = 1.2
Since C''(x) is positive for all values of x, we know that the critical point x = 310 corresponds to a minimum.
Therefore, the number of machines that must be made to minimize the unit cost is 310.