Answer:
The answer is: $5,000
Step-by-step explanation:
Greller first bought 100 stocks at $100 each ($10,000 in total).
Then the stock split in two, so Greller now had 200 stocks with a basis of $50 each.
If then Greller sold 100 stocks, the total basis for the sell is $5,000.
Any amount above $5,000 will be considered as capital gains by the IRS. So Greller should report the $1,500 he earned.