Assuming this is a right triangle, we can use the Pythagorean theorem:
[tex](length-of-leg-1)^2+(length-of-leg-2)^2=(length-of-hypotenuse)^2\\12^2 + 7^2 = (length-of-hypotenuse)^2\\193 = (length-of-hypotenuse)^2\\length-of-hypotenuse = \sqrt{193}[/tex]
Thus x = [tex]\sqrt{193}[/tex]
Hope that helped!
