Anuj and Ashish launched a new fountain pen in their pen-factory which is consisting of ₹ 6400/- as…

Anuj and Ashish launched a new fountain pen in their pen-factory which is consisting of ₹ 6400/- as overheads, ₹ 35/- per pen as the cost of material and labour cost, ₹ $\frac{x^2}{100}$ for $x$ items produced. Find the values of $x$ for which average cost is increasing.