You didn't state how many classes you were to use.  Usually you
want 6 or 7 classes.

If you want 6 classes, then

Subtract 64 - 23, get 41

Divide 41 by 6, get 6.833333333333, round UP to two places 6.84
(even though the usual rounding would be down to 6.83, we must
round UP to 6.84.)

To find the beginning of the first class, since you are to round to
two decimal digits, subtract .01 from the least number: 23-.01 = 22.99

22.99 -- 29.83
29.83 -- 36.67
36.67 -- 43.51
43.51 -- 50.35
50.35 -- 57.19
57.19 -- 64.03
--------------

If you want 7 classes, then

Subtract 64 - 23, get 41

Divide 41 by 7, get 5.857142857, round UP to two places 5.86.

To find the beginning of the first class, since you are to round to
two decimal digits, subtract .01 from the least number: 23-.01 = 22.99

22.99 -- 28.85
28.85 -- 34.71
34.71 -- 40.57
40.57 -- 46.43
46.43 -- 52.29
52.29 -- 58.15
64.01 -- 69.87
--------------

So the class width is 6.84 if you want 6 classes and
the class width is 5.86 if you want 7 classes.

Edwin