Answer: For the $18 sweatshirt, DISCOUNT 2 is the best.
For the $30 sweatshirt, DISCOUNT 3 is the best.
Step-by-step explanation: For the $18 sweatshirt, 20% off would be $14.4. If she uses the $5 rebate, shes getting $5 off or back. She can't use the 3rd discount because it's not over $20.
For the $30 sweatshirt, 20% off of that makes it $24. $5 back from the rebate makes it $25, and half off (50%) makes it $15. Which is the cheapest.