Remove the wood block from the water. Place the brick block into the water and let it sink. How much water does the brick block displace? Hint: This is the liquid level with the block minus the liquid level before the block is added.

the volume desalinated  that is placed is equal to the volume of the block.

Explanation:

For this exercise we use the Archimedean principle which states that the thrust is equal to the weight of the desalted liquid.

                      B = ρ g V

When we have the block of wood the volume of water desalinated in the volume of the block under water, this is because the wood floats in the water

When placing the block of clay (brick), it sinks, so the volume desalinated  that is placed is equal to the volume of the block.

          V_body = V_waer = l to h

the total distance traveled by the car is

30km + 49km = 79 km .