Answer :
The general formula to know how much is the sum of the interior agles of a polygon is:
[tex](n-2)\cdot180º[/tex]Where n is the number of sides.
Then:
In a polygon with 3 sides the internal angles sum: 180º
[tex](3-2)\cdot180º=180º[/tex]In a polygon with 4 sides the internal angles sum: 360º
[tex](4-2)\cdot180º=360º[/tex]In a polygon with 5 sides the internal angles sum: 540º
[tex](5-2)\cdot180º=540º[/tex]