The table shows information about the lengths of some leaves collected by a class. Length (l cm): \(10 < l \le 12\), \(12 < l \le 14\), \(14 < l \le 16\), \(16 < l \le 18\), \(18 < l \le 20\). Frequency: 4, 9, 15, 11, 3. A frequency polygon is drawn for this information on the grid. Write down the coordinates of the five points that must be plotted, in order, before they are joined with straight lines.