Pythagorean theorem: find the perimeter

The answer is 5
Explanation:
We need to use the Pythagorean,
a^2 + b^2 = c^2
Where c is the hypotenuse
We can fill in spots now 12^2 + b^2 = 13^2
And then we solve 144 + b^2 = 169
Next we get b^2 alone
169-144=25
So we get b^2=25
For the final step you have to find the square root of 25 to get b alone which is 5