I have this accounting problem that says "Issued check number 30564 and purchased office equipment with a list price of $2,100 and trade discounts of 30% and 10%". Do I multiply $2,100 by 0.70 and then multiply that result by 0.90? Or do I multiply $2,100 by 0.70 and add to it $2,100 multiplied by 0.90?