Consider that the volume of a rectangular prism is L X W X H (length times width times height).
Let's call the volume of the smaller solid = V1. Then, V1 = L1 * W1 * H1
Let's now call the volume of the larger solid V2. Then V2 = L2 * W2 * H2
We know from the problem that H1 = H2
We also know that L1 = 1/2 L2, and W1 = 1/2 W2
Therefore, we can express V1 as 1/2 L2 * 1/2 W2 * H2 = 1/4 * L2 * W2 * H2
You should now be able to determine how much greater the volume of the larger solid is compared to the smaller solid.