In the Argand plane, the vector $z=4-3i$  is turned in the clockwise sense through ${180}^0$  and  stretched three times. The complex number represented by the new vector is:

$\left|z\right|=\sqrt{4^2+{\left(-3\right)}^2}=5$ 

Let $z_1$  be the new vector obtained by rotating $z$  in the clockwise sense through ${180}^0$ , therefore,

    $z_1=e^{-i\pi }z=\left(\cos \pi -i\sin \pi \right)z$ , i.e., $z_1=-4+3i$

The unit vector in the direction of $z_1=-4+3i$ ,is $-\frac{4}{5}+i\frac{3}{5}$

Therefore, required vector

      $=3\left|z\right|\left(-\frac{4}{5}+\frac{3}{5}i\right)=15\left(-\frac{4}{5}+\frac{3}{5}i\right)=-12+9i$