Hi. Would someone be able to explain why we are dividing the total area for a regular 9-sided polygon by 9 to get the area of the given figure? The given figure is not a regular polygon (i.e. it is not an equilateral triangle), so how can we determine that the height is the same as the regular nine-sided polygon? Maybe, I am missing something.

Whoever can solve this question, I declare the math god who will ace the GRE Quant section!