The picture isn’t clear so I can’t read the dimensions of the box but I can try my best to guide u through the question.
For part a u need to find the volume of the box as that will equal the volume of sand that can be filled inside.
For this u multiply the height, width and length of the box.
For part b the mass of sand alone will be
=Mass of box + sand - Mass of empty box
=216 - 40
=176 grams
For part c the density of sand can be calculated by the formula
Density= Mass/Volume
So the mass (176g) / volume from part a
For part d u need to know that something will float if it has a lower density than what it is floating in. If the final density of sand that was found in part c is less than the density of gold (19.3 g/cm^3) it will float. Otherwise it will sink.
Hope this helped!