2023 Gauss 8 Problem 2

The graph shows the forecast wind speed (in km/h) during a 7-day period. Jack can sail alone only when the forecast wind speed is less than 20 km/h. During this 7-day period, on how many days will Jack be able to sail alone?

\textbf{(A)}\ 4\quad \textbf{(B)}\ 6\quad \textbf{(C)}\ 1\quad \textbf{(D)}\ 2\quad \textbf{(E)}\ 5

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Gauss contests here.