Can you guide me through solving this problem: Simon wanted to buy flowers that his mom could plant for Mother's Day.  The garden center was offering 10% off all purchases.  He bought 5 pansies at $2.50 each, one hydrangea that cost $12.50 and 5 petunias that cost $1.00 each.  If he paid with a $50 bill, how much change would Simon receive back from his purchase?