Set up System of equations, use appropriate method to solve and define variables

Question

A factory produces 2 types of cogs in 2 different factories. Factory a produces 25 standard and 50 delux cogs per day. Factory b produces 150 standard and 75 delux cogs per day. How many days  should the company operate each factory in order to exactly fill an order for 500 standard and 325 delux cogs?