Ontario Mathematics Proficiency Practice Test

To find the total surface area of a cube, the formula used is \( 6a^2 \), where \( a \) represents the length of an edge of the cube. In this case, the edge length is given as 3 cm.

First, you would square the length of the edge:

\[

a^2 = 3 \text{ cm} \times 3 \text{ cm} = 9 \text{ cm}^2

\]

Next, since a cube has 6 faces, you multiply the area of one face by 6:

\[

\text{Surface Area} = 6 \times 9 \text{ cm}^2 = 54 \text{ cm}^2

\]

Thus, the total surface area of the cube is 54 cm². This calculation is consistent with the correct choice. The way the formula derives from the properties of a cube ensures that all six faces are accounted for in the surface area.