Simple,
2.) If a circle is divided into 9 parts and your are trying to find three of those parts, first find what is 1 of those parts...
In a circle there is 360°
360/9=40
That is 1 part.
For three parts it would be 40*3=120
Your answer is 120°
3.) Do the same thing here.
A circle is 360°
360/10=36
Now, for four of those parts...
36*4=144
The answer is 144°.
