Formula for the number of triangles :
$$\frac{n \times m \times (n + 1)}{2}$$ where n = number of vertical parts and m = number of horizontal parts.
So , this figure has 2 triangles with 2 vertical parts and 3 horizontal parts.
Using the formula :Â $$\frac{2 \times 3 \times (2 + 1)}{2}Â \times 2$$ = 18
So , the answer would be option b)18.
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