So basically you counting by 3
Convex Polygons

All of its angles are less than 180°.
All of the diagonals are internal.
Concave Polygons

At least one angle measures more than 180°.
At least one of the diagonals is outside the shape of the polygon.
Equilateral Polygons

All sides are equal.
Equiangular Polygons

All angles are equal.
Regular Polygons

They have equal angles and sides
Irregular Polygons
They do not have equal angles and sides.
Types of Polygons based on Number of Sides
Triangle

3 sides.
Quadrilateral

4 sides.
Pentagon

5 sides.
Hexagon

6 sides.
Heptagon

7 sides.
Octagon

8 sides.
Enneagon or Nonagon

9 sides.
Decagon

10 sides.
Hendecagon

11 sides.
Dodecagon

12 sides.
Tridecagon or triskaidecagon

13 sides.
Tetradecagon or tetrakaidecago

14 sides.
Pendedecagon

15 sides.
Hexdecagon

16 sides.
Heptdecagon

17 sides.
Octdecagon

18 sides.
Enneadecagon

19 sides.
Icosagon

20 sides.
Answer:
Step-by-step explanation:
The formula for the area of a triangle is 
The triangles that can be made is the triangle that has legs 20 and 50 and the triangle that has legs 20 and 10.
Since there are 2 of each triangles, we get:
The answer that fits is the first option.
