Answer:
12
Step-by-step explanation:
The first step that I would take is fine the 3,6, triangle using the pythagoras theorem.
[tex]\sqrt{9+36} =\sqrt{45}[/tex]
We should also set a variable for the last side we haven't figured out yet (I will refer to it as y)
so here is what we know
[tex]45+y^2=(3+x)^2\\\\x^2+36=y^2[/tex]
notice how both equations have [tex]y^2[/tex] this should give you a hint as to what to do
[tex]y^2=(3+x)^2-45\\\\y^2=x^2+36[/tex]
therefore
[tex](3+x)^2-45=x^2+36[/tex]
now solve for x
[tex](3+x)^2-45=x^2+36\\\\x^2+6x+9-45=x^2+36\\\\x^2+6x-36=x^2+36\\\\6x=72\\\\x=12[/tex]
