The volume of the tetrahedron included between the plane $3x+4y-5z -60 =0$ and the coordinate planes in cubic units is

Vertices of the tetrahedron are

$(0,0,0),(20,0,0),(0,15,0)$ and $(0, 0, 12)$

so its volume is $\frac{1}{6}\left|\begin{array}{cccc}0& 0& 0& 1\\ 20& 0& 0& 1\\ 0& 15& 0& 1\\ 0& 0& 12& 1\end{array}\right|\mid =600$

cubic units.