\[\boxed{\text{154\ (154).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[x = 10\ см;\ \ m = 700\ грамм.\]
\[m = \rho V;\ \ \ V = x^{3};\]
\[\Longrightarrow m = \rho x^{3} \Longrightarrow \ \rho = \frac{m}{x^{3}} =\]
\[= \frac{700}{10^{3}} = 0,7.\]
\[Значит,\ m(x) = 0,7x^{3}.\]
\[\textbf{а)}\ x = 2:\ \ \ m \approx 5,4;\]
\[x = 5:\ \ \ m \approx 87;\]
\[\textbf{б)}\ m = 30:\ \ \ x \approx 3,5;\]
\[m = 100:\ \ \ x \approx 5,2.\ \]