As, number of Observation=45
Minimum value>0
And Maximum value<29
I would prefer classes from[0-3,3-6,6-9,9-12,12-15,15-18,18-21,21-24,24-27,27-30] or[0-5,5-10,10-15,15-20,20-25,25-30].
So YOU can choose either 10 classes or 6 classes.
As 6 classes will be perfect because number of observation is quite large so each class will contain adequate number of observations and you can draw any kind of graph easily.