What is the volume of a cube that has a face diagonal of 5cm { to the nearest whole number

The diagonal forms a right isosceles triangle whose hypotenuse is x√2 where x is the length of a side of the square face
so, x√2=5
x=5/√2
x=5/1.414
x=3.536 cm
you can also use the Pythagorean Theorem to get the length of a side, x
5^2=x^2+x^2
25=2x^2
x^2=25/2
x^2=12.5
x=√12.5
x=3.535 cm
the volume is V=3.536^3
V=3.536*3.536*3.536
V=44.2 cm^3
my answer has more accuracy, therefore you choose D) which is closest to my answer