in this problem B. ত্রিভুজের ভেতর বৃত্ত . I think ,no two prime satisfies the equation \frac{b^2}{a}×(a^{2}−π)(a− \sqrt{b})
Read the problem statement and give another try! 
I think the area of the dark region is 2.07… , am I right?
but the equation gives 1.035042998614011 for 2 and 3.
b^2×(a^2−π)(a−\sqrt{b}
) = 2.07.. for 2 and 3.