3. 1080°
4. 900°
You can easily find the sum of interior angles by this equation: (n-2)180°
N=The number of sides of the polygon
So, in picture 3, the polygon has 8 sides. If we substitute this value into the equation, (8-2)180= 1080° !
The same in picture 4, with 7 sides, (7-2)180= 900°
have a nice day!