Given that the total profit is determined using the equation:
P=7.5n-(2.25n+15)
The minimum cost of necklace will be found as follows:
writing the above is straight line form of y=mx+c, where m is the slope and c is the y-intercept we get
P=7.5n-2.25n-15
P=5.25n-15
thus the slope is 5.25
the y-intercept is at (0,-15)
the minimum amount is 15
Answer: C. $15