The number of computer purchases is 5000 times /x, because it costs 1600 yuan each time, so this part of the cost is 5000 * 1600 times/x.

The annual storage fee rate is 10%, so the storage fee is 10%x/4000.

y=8000000/x+x/40000

Take the derivative so that y' = 0.

When the extreme point is x=200, other expenses are the lowest when buying 200 sets each time.