Answer:
12 ft
Explanation:
Assuming the triangle is a right triangle, we can use the Pythagorean theorem, a^2+b^2=c^2
Plugging our numbers in, we get 5^2+b^2=13^2
25+b^2=169
b^2=144
b=12
I also believe that this is a 5 12 13 triangle so if you remember those, you can automatically know the lengths!