Barring any other income tax bracket, Health tax, etc.

Jack and Jill buy 200 shares of stock for $5000, $25 per share

The share price went up to $50 per share and the stock is now worth $10,000

it splits 2 for 1…they now have 400 shares worth $10,000 @ $25 per share

they sell the 400 shares:

a. is there cost basis still $5,000 (sold 400 shares for $10k) and will pay capital gains on 5k profit?

or…

b. is there cost basis less than the $5000 and will pay more in capital gains since the stock split?

thank you.
Douglas