Football teaser probability question

What percentage of games must you win to show a profit betting football teasers? Assume you are laying $11 to win $10 and you must go 2 for 2 to win the wager.
Thank you GG.

[Roscoe]

To break even, you would need to hit both games 11/21 (52.38% of the time). For each game, you would need to hit approximately 72.375% of the time.

I understand the 11/21 figure but how did you come up with 72.375%?

[Roscoe]

I took the square root of 11/21.