Question 42613
Ok for this we have to use the Pythogrean Theorem which is A^2+B^2=C^2

So like the problem said, C, is the longest side while A and B are the shorter sides which in this problem are 3 and 4.

So...
3^2+4^2=C^2
9+16= C^2
25=C2

Now that we have found what C^2 is, we need to find the square root of C^2, and that is 5, so the missing side of your triangle is 5.