The formula for the volume of a sphere is
V = (4/3)π*r^3
The radius is given as 6 in, so the volume of one pillow is
V = (4/3)π(6 in)^3 = 288π in^3
and the volume of two (2) of them will be
V = 2*(288π in^3) = 576π in^3
V ≈ 1810 in^3 . . . . . . . . . matches selection C