Since we are dealing with a right triangle, we can use the Pythagorean theorem, shown below
[tex]\begin{gathered} H^2=L^2_1+L^2_2 \\ H\to\text{ hypotenuse} \\ L_1,L_2\to\text{ legs} \end{gathered}[/tex]
In our case,
[tex]\begin{gathered} H=15,L_1=3 \\ \Rightarrow L^2_2=15^2-3^2=216 \\ \Rightarrow L_2=\sqrt[]{216}=14.6969\ldots\approx14.697 \\ \Rightarrow L_2=14.697 \end{gathered}[/tex]
The answer is 14.697
