SOLUTION
From the given right triangle, using Pythagorean theorem, it follows:
[tex]AC^2=AB^2+BC^2[/tex]
Substitute AB = 12 and AC = 31 into the equation:
[tex]31^2=12^2+BC^2[/tex]
Solve for BC:
[tex]\begin{gathered} 961=144=BC^2 \\ BC^2=961-144 \\ BC^2=817 \\ BC=\sqrt{817} \\ BC\approx29 \end{gathered}[/tex]
Therefore the required answer is 29
