The owner of an electronics store buys 150 noise cancelling headphones for $20 each. He marks up the price of the headphones by 75%. The store sells 65 headphones at full price. The owner then discounts the headphones 20% off of the original selling price. The store sells another 45 headphones at this price.

a. What profit has the store owner made so far on the sale of the headphones?

b. If sales tax is 7.8%, how much money has the store owner collected in sales tax?