Given:
The cost function is C(x) = 10x + 3000.
Step-by-step explanation:
The equation for the average cost is,

The inequality for x is,

Solve the inequality for x.
[tex]\begin{gathered} \frac{10x+3000}{x}\cdot x<30\cdot x \\ 10x+3000-10x<30x-10 \\ \frac{3000}{20}<\frac{20x}{20} \\ 150
So the number of items should be more than 150.