For the data shown on the following table, determine the arithmetic mean speed and the median speed as well as the $85\%$ speed, draw the cumulative and frequency distribution curves

$\backslash$table$[[$Speed group, $K\frac{m}{h}r,20-29\mathrm{.}9,30-39\mathrm{.}9,40-49\mathrm{.}9,50-59\mathrm{.}9,60-69\mathrm{.}9,70-79\mathrm{.}9$