\[\boxed{\mathbf{Страница\ 74.\ }\mathbf{Еуроки\ - \ ДЗ\ без\ мороки}}\]
\[\boxed{\mathbf{12.\ }}\]
\[1\ дм \Longrightarrow 6 \cdot 1^{2} = 6\ дм^{2}.\]
\[20\ см \Longrightarrow 6 \cdot 20^{2} = 6 \cdot 400 =\]
\[= 2400\mathbf{\ }см^{2} = 24\ дм^{2}.\]
\[300\ мм \Longrightarrow 6 \cdot 300^{2} =\]
\[= 6 \cdot 90\ 000 = 540\ 000\ {мм}^{2} =\]
\[= 5400\ см^{2} = 54\mathbf{\ }дм^{2}.\]
\[24\ :6 = 4\ раза.\]
\[54\ :6 = 9\ раз.\]
\[Ответ:в\ 4\ раза,\ \ \ в\ 9\ раз.\]
\[\boxed{\mathbf{13.\ }}\]
\[\textbf{а)}\ (87 - 16) \cdot 5 = 355\]
\[\textbf{б)}\ 19 \cdot 4 - 28 = 76 - 28 = 48\]
\[\textbf{в)}\ (85\ :5 + 96) \cdot 3 =\]
\[= (17 + 96) \cdot 3 = 113 \cdot 3 = 339\]
\[\textbf{г)}\ (9 \cdot 12 + 33) \cdot 2 - 12 \cdot 6 =\]
\[= (108 + 33) \cdot 2 - 72 =\]
\[= 141 \cdot 2 - 72 = 282 - 72 =\]
\[= 210\ \]