[tex]\boxed{\begin{array}{l}\tt 1)\\\rm a)~\sf 0,00035=3,5\cdot10^{-4}\\\rm b)~\sf157~000~000=1,57\cdot10^8\\\tt 2)\\\rm a)50~km=50~000~m\\\rm b)~3,8~h=228~min\\\rm c)~\sf 72km/h\div3,6=20~m/s\\\tt 3)\\\sf \Delta\,t=45min\div60=\dfrac{3}{4}h\\\sf \Delta\,s=s-s_0\\\sf\Delta\,s=80-30\\\sf\Delta\,s=50~km\\\sf v=\dfrac{\Delta\,s}{\Delta\,t}\\\sf v=\dfrac{50}{\frac{3}{4}}\\\sf v=50\cdot\dfrac{4}{3}\\\sf v=66,66~km/h\end{array}}[/tex]
