$Q_1$ of the data 14, 7, 13, 12, 13, 17, 8, 10, 6, 15, 18, 21, 20 is

Ascending order of data is $6,87,8,10,12,13,13,14,15,17,18,20,21$

$n=13,\frac{n+1}{4}=\frac{13+1}{4}=\frac{14}{4}=\frac{7}{2}=3.5$

$\therefore Q_1=$ average of 3^rd and 4^th items $=\frac{8+10}{2}=9$