Cesar Rego Computers, a Mississippi chain of computer hardware and software retail outlets, supplies both educational and commercial customers with memory and storage devices. It currently faces the following ordering decision relating to purchases of very high$-$density disks:

D $=36000$ disks

S $=$ $$25$

I $=20\%$

Purchase price $=$ $$0\mathrm{.}85$

Discount price $=$ $$0\mathrm{.}82$