Final answer:
To keep crate d in equilibrium, the mass of block c should be equal to the mass of the water displaced by crate d.
Step-by-step explanation:
In order for crate d to be in equilibrium, the forces acting on it must be balanced. One of the forces acting on crate d is the weight of block c. To keep crate d in equilibrium, the mass of block c should be equal to the mass of the water displaced by crate d.
To find the mass of the water displaced, we can use the density of water and the volume of water displaced by crate d. The formula to calculate the mass of water displaced is mass = density × volume.
Once we have the mass of the water displaced, we can set that equal to the mass of block c to find the value that represents the mass of block c that would keep crate d in equilibrium.