For this problem, we could use the pythagorean theorem as follows:
The pythagorean theorem states that the square of the hypotenuse equals to the sum of the square of each one of the sides of the triangle:
[tex]\begin{gathered} x^2=7^2+14^2 \\ x^2=49+196 \\ x^2=245 \end{gathered}[/tex]
Finally,
[tex]x=\sqrt[]{245}[/tex]
So, the number that you must put in the green box is 245.
