\[\boxed{\mathbf{804\ (804)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\boxed{\ \mathbf{804}\mathbf{\ (625)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]
\[c = 20\ см;\ \ \ \ \]
\[a = c + 4 = 20 + 4 = 24\ см;\]
\[b = c\ :5 = 20\ :5 = 4\ см.\]
\[V = abc = 24 \cdot 4 \cdot 20 =\]
\[= 24 \cdot 80 = 1920\ см^{3}.\]
\[Ответ:1920\ см^{3}.\]