Question 20Corners are sliced off a unit cube so that the six faces each become regular octagons. What is the total volume of the removed tetrahedra?$\dfrac{5\sqrt2-7}{3}$$\dfrac{10-7\sqrt2}{3}$$\dfrac{3-2\sqrt2}{3}$$\dfrac{8\sqrt2-11}{3}$$\dfrac{6-4\sqrt2}{3}$