How to collect 'C'-common factor for d'

Dear student
as you want to know about common factor (c), it could be 2.
(iii) short cut method

height	X-A(A=69) d- 69	d' = d/c c = 1
64	64 - 69 = -5	-5/1= -5
59	59-69=-10	-10/1 = -10
67	67-69=-2	-2/1= -2
69	69-69=0	0
65	65-69= -4	-4/1= -4
70	70-69=1	1/1= 1
68	68-69 = -1	-1/1 = -1
		sum of d'= -21

mean = A + sum of d' X c / n
         = 69 + (-21 X 1)/7
        = 69 -21/7
      = 69 -3
     = 66
​​​​​​(i) direct method
     mean = sum of all observation/ no. of observation
              = (64+ 59+67+69+65+70+68)/7
             = 462 / 7
             = 66
(ii) short cut method 

heights(x)	X-A(A=69) (d)
64	64-69= - 5
59	59-69= -10
67	67-69= -2
69	69-69=0
65	65-69= -4
70	70 - 69 = 1
68	68 - 69 = -1
n=7	sum of d = -21

mean = A + (sum of d)/ N
          = 69 + (-21)/ 7
         = 69 -3
           = 66

Regards