Answer: On Monday, Heather had 32 hats.
Step-by-step explanation: After Heather bought six hats on Tuesday, she had double the amount of 19, since half of her hats were destroyed on Wednesday resulting in 19 left. Double of 19 is 38 hats, meaning she had 38 after she bought six on Tuesday. That means on Monday she had 38 - 6 = 32.