The solid below is made up of 1-cm cubes. What is the least number of cubes that needs to be added to the solid to make it a cube? Answer : ___

1. Determine the dimensions of the smallest possible cube that can enclose the solid.

The maximum height of the solid is $4$ cubes.
The width consists of a left column, a middle column, and a right column, making it $3$ cubes wide.
The depth consists of the back column and a row of $3$ cubes extending forward, making it $1 + 3 = 4$ cubes deep.
To form a cube, all dimensions must be equal to the largest dimension, which is $4$. Thus, the target cube must be $4 \times 4 \times 4$.

2. Calculate the total number of cubes required for the $4 \times 4 \times 4$ cube.

Total cubes needed $= 4 \times 4 \times 4 = 64$

3. Count the number of cubes currently in the solid.

Number of cubes $= 4 \text{ (tallest column)} + 3 \text{ (left column)} + 2 \text{ (right column)} + 3 \text{ (forward row)} + 1 \text{ (in front of tallest)} + 1 \text{ (between columns)} = 14$

4. Calculate the number of cubes to be added.

Cubes to add $= 64 - 14 = 50$