A cumulative frequency table gives the number of cyclists with a speed below each value…

Step 1. The frequencies. The classes $0$ to $10$, $10$ to $20$, $20$ to $30$, $30$ to $40$ and $40$ to $50$ have $6$, $18 - 6 = 12$, $41 - 18 = 23$, $57 - 41 = 16$ and $64 - 57 = 7$ cyclists.

Step 2. The median class. $\dfrac{N}{2} = 32$. The running total is $18$ before $20$ and $41$ before $30$, so the median class is $20$ to $30$.

Step 3. The median. $l = 20$, $cf = 18$, $f = 23$ and $h = 10$. So $\text{median} = 20 + \dfrac{32 - 18}{23} \times 10 = 20 + 6.087 = 26.09$ km/h.