How does the stake factor into sports betting winnings

How does my sports betting stake factor into filing my sports bad betting winnings?

 

let’s say I bet $100 to win $50 and win my bet. The online sportsbook pays me $150. So I won $50 and got my $100 bet back. 

how do I report these winnings to the IRS? Is it $50 in winnings or $150? If it’s $150 in winnings can the original stake of $100 be deducted on my taxes?