[tex]-4-(-4)+(-4)-4+(-4)+12=-4+4-4-4-4+12=0-12+12=0[/tex]
[tex]S=294cm^2\\S=6a^2\implies a^2=\cfrac{S}{6}\implies a=\sqrt{\cfrac{S}{6}}\\V=a^3=\left(\sqrt{\cfrac{S}{6}}\right)^3=\left(\sqrt{\cfrac{294cm^2}{6}}\right)^3=\left(\sqrt{49cm^2}\right)^3=\left(7cm\right)^3=343cm^3[/tex]