Answer:
$4,000
Step-by-step explanation:
Penny's originally purchased 2,000 stocks
she then received 5% stock dividends, which means that her total stocks were 2,100
then the stock split 2 for 1, so Penny had 4,200 stocks in total
stocks basis = $10.50 x 2,000 = $21,000
basis per stock = $21,000 / 4,200 stocks = $5 per stock
basis for 800 stocks sold = $5 x 800 = $4,000