She got a 20% discount (or 80% discount). (Work shown for 80%). First you have to find out how much Mandy paid. So from 15000 you will subtract 3000. 15000-3000=12000. Next you need to set up your equation. . You then have to cross multiply. So 100 times 12000, 100*12000=1200000. And 15000 times x is 15000x. Finally you divide both sides by 15000. And 1200000 divided by 15000 is 80. X=80