The range of the data: $25, 18, 20, 22, 16, 6, 17, 15, 12, 30, 32, 10, 19, 8, 11, 20$ is

The lengths of $62$ leaves of a plant are measured in millimetres and the data is represented in the following table:

Length (in mm)	Number of leaves
$118-126$	$8$
$127-135$	$10$
$136-144$	$12$
$145-153$	$17$
$154-162$	$7$
$163-171$	$5$
$172-180$	$3$

Draw a histogram to represent the data above.

The class-mark of the class $130-150$ is:

The following are the marks (out of $100$) of $60$ students in mathematics:
$16, 13, 5, 80, 86, 7, 51, 48, 24, 56, 70, 19, 61, 17, 16, 36, 34, 42, 34, 35, 72, 55, 75, 31, 52, 28, 72, 97, 74, 45, 62, 68, 86, 35, 85, 36, 81, 75, 55, 26, 95, 31, 7, 78, 92, 62, 52, 56, 15, 63, 25, 36, 54, 44, 47, 27, 72, 17, 4, 30$
Construct a grouped frequency distribution table with a class width of $10$,such that one of the classes is $10-20$ ($20$ not included).

In a frequency distribution,the mid value of a class is $10$ and the width of the class is $6$. The lower limit of the class is:

The observations $7, 15, x-1, x+1, 24, 28$ have been arranged in ascending order. If the median of the data is $21$,find the value of $x$.