for this problem :

Calculate the volume of the tetrahedron whose vertices are y=0, z=0, x=0 και y-x+z=1

this integral is it the corect one ?

$\displaystyle \int_{x=0}^{1}\int_{y=0}^{-y+1}\int_{z=0}^{z=x-y+1}dG=\int_{0}^{1}\int_{y=0}^{-y+1}(x-y+1) dydx$