\[\boxed{\text{181\ (181).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ v = s\ :t\]
\[v = \frac{600}{t}\ \frac{км}{ч}.\]
\[\textbf{б)}\ t = s\ :v\]
\[t = \frac{600}{v}\ (ч).\]