In a long jump, three boys jump together from a particular spot. One boy covers a distance of $10 \mathrm{cm}$, second covers $50 \mathrm{cm}$ and third covers $70 \mathrm{cm}$. If the minimum distance is $\mathrm{k} \mathrm{cm}$, each should cover so that all can cover the distance in complete steps. Find the value of $k$