$a-\frac{1}{a}$=3 হলে $a^3-\frac{1}{a^3}$ এর মান কত?

A customer came to a shop and asked the shop manager to give a 20% discount on the listed price of a pen. Moreover, for every 10 pens purchased, he wanted two pens free of cost. The manager agreed to the customer's offer because he could still make a profit of 20% on the cost price of a pen. What was the listed price of the pen?

The fee for a course was increased by x percent from that of the previous year. Arif, a meritorious student, got y percent waiver on his course fee for his extraordinary performance. If the fee collected from Arif is 80% of the course fee of the previous year, what is the value of yyy in terms of xxx?