As the word suggests, a quarter-sphere is a quarter of a sphere, and thus the volume of a quarter-sphere is a quarter of the volume of the sphere.
The volume of a sphere is computed as

So, the volume of a quarter-sphere is

do parentheses first which gives you 42-4+111 then aubtract to get 38+111 which equals 149
The correct answer is C.
Because: 2.9 multiplied by 10 bags equals 29cubic ft and she needs 30 cubic ft. So she would need to buy 11 bags to make sure she has enough sand for the whole thing. 11 x 2.9 = 31.9 which ensures she has enough for the whole thing including extra in case. So you answer would be Answer C.