For this case we have by definition, that the volume of a cone is given by:

Where:
A: It is the cone radius
h: It's the height
They tell us that the diameter is 21 m, then the radius is half the diameter, that is: 10.5m. The height is 4m. Substituting the data:
.
Finally, the volume of the cube is
ANswer:
Option B
The probability that student scored more than 850 we shall proceed as follows:
z=(x-μ)/σ
where:
x=850
μ=750
σ=50
thus
z=(850-750)/50
z=2
thus
P(x>850)=1-P(x<850)=1-P(z<2)=1-0.9772=0.0228
Answer: P(x>850)=0.0228