[tex]V=P_p\cdot H\\\\P_p=\frac{1}{2}\cdot(a+b)\cdot h\\\\a=12, \ b=4, \ h=3\\\\P_p=\frac{1}{2}\cdot(12+4)\cdot3=8\cdot3=24 \ [ \ j^2 \ ]\\\\H=7\\\\V=24\cdot7=\boxed{168 \ [ \ j^3 \ ]}[/tex]