Here the number of spokes are increasing and the angle between a pair of consecutive spokes is decreasing. So, it is a inverse proportion and angle at the centre of a circle is 360 degree.
When the number of spokes is 8, then angle between a pair of consecutive spokes = 360/8=45 degree
When the number of spokes is 10, then angle between a pair of consecutive spokes= 360/10=36 degree
When the number of spokes is 12, then angle between a pair of consecutive spokes= 360/12=30 degree.

(i) Yes, the number of spokes and the angles formed between a pair of consecutive spokes is in inverse proportion.
(ii) When the number of spokes is 15, then angle between a pair of consecutive spokes = 360/15=24 degree.
(iii) The number of spokes would be needed = 360/40=9 degree