Plz tell (a) part

Dear Student,
​​As per the question, class mid-points in a frequency distribution of a group of a person are 125, 132, 139, 146, 153, 160, 167, 174 and 181
size of class interval(h) = difference between two consecutive mid values
h = 132 - 125
h = 7
Therefore, the class size is 7.
Regards,
Priyanka