PLEASD HELP!!! I have no clue how to do this

Step-by-step explanation:
[tex]for1 \\ x =8 \\ y = x \sqrt{2} = 8 \sqrt{2 } = 11.31[/tex]
[tex]for2 \\ x =25 \sqrt{2} = 35.36 \\ y = 25[/tex]
[tex]for3 \\ 19 = x \sqrt{2} \\ x = \frac{19}{ \sqrt{2} } = 13.44 \\ y = 13.44 \\ [/tex]