Answer:
:
To find the number of machines that must be made to minimize the unit cost, we need to find the minimum value of the function C(x). To do this, we can take the derivative of C(x) and set it equal to zero:
C'(x) = 2x - 680
2x - 680 = 0
x = 340
Therefore, the minimum value of C(x) occurs when x = 340, and 340 machines must be made to minimize the unit cost.