a ≅ 11.6 ft
Pythagorean theorem
c²-b²=a²
c²-a²=b²
a²+b²=c²
Now since we're trying to find a leg we'll use the first equation
c²-b²=a²
Plug in the hypotenuse for c and the leg for b
12²-3²=a²
144-9=a²
135=a²
Now square root both sides
[tex]\sqrt{135}[/tex] = [tex]\sqrt{a^{2} }[/tex]
[tex]3\sqrt{15}[/tex]= a
a ≅ 11.6 ft