Question on Risk and Uncertainty

Sam is a trader who sells Parle G biscuits. He generally buys the biscuits in quantities
to avail the quantity discount. The purchases can be made in the multiples of 500
packets only. If the quantity purchased is 1000 or less per month, the purchase price is
$6 per packet, but above 1000 packets per month, the purchase price is $5 per packet.
Sam sells the biscuits at $8 per packet. The shelf life of the biscuits is 1 month, and
after that, the company buy back the unsold biscuits at $1 per packet.
For every unsatisfied customer, the opportunity cost is calculated as $0.5. The
demand for the biscuits could be 1000, 1500 or 2000, with probabilities of 0.1; 0.3
and 0.6 respectively.
Required:
1. Advise Sam on the quantities to buy under the following decision criteria.
a. Maximin
b. Maximax
c. Mini max regret
d. Expected value

In this question could you please explain what do we do with the “unsold biscuits buy-back cost” and the “opportunity cost for unsatisfied customer that is $0.5”

Thank you!