Let 'p' represent the number of pants and let 's' represent the umber of shirts.
Since the store can buy up to a total of 500 pants and shirts each month, the first inequality is:
then, the store wants to buy at least as many shirts as pants, then this can be represented with the following inequality:
finally, the store wants to buy at least 100 pants each month, then:
therefore, the system of inequalities is: