Given equation of sphere is
$x^{2}+y^{2}+z^{2}-12 x-4 y-3 z=0$
$\therefore $ Centre of sphere is $\left(6,2, \frac{3}{2}\right)$.
$\therefore $ Radius of sphere $=\sqrt{(6)^{2}+(2)^{2}+\left(\frac{3}{2}\right)^{2}}$
$=\sqrt{36+4+\frac{9}{4}}=\sqrt{\frac{169}{4}}$
$=\frac{13}{2}$