For this question, we use the Pythagorean theorem.
[tex]a^2+b^2=c^2[/tex]
We know the lengths of the legs, a and b.
[tex]a=3[/tex]
[tex]b=4[/tex]
Now, let's solve for the hypotenuse, c.
[tex]3^2+4^2=c^2[/tex]
[tex]25=c^2[/tex]
Take the positive square root.
[tex]\boxed{c=5}[/tex]
Hope this helps! :)