OG Practice Test 1, Quant Q23

I understand how to solve this question, however, I was using r/2 for the base when I calculated the area of the equilateral triangle. The explanation used r, which is the hypotenuse. Why can’t I use r/2? How do I know when to use the hypotenuse value versus the base value?
Thank you

You use the the 30:60: 90 ratio to find the sides . But when use the formula 1/2 x b x h to calculate the area you have to take the base of the whole triangle and not just of the right triangle that you calculated the value for.

I should have noticed that! Thank you