There are 6 sides on the rectangular prism. Two sides have length × width dimension. Two sides have length × height dimension. Two sides have width × height dimension. To find the surface area, we need to find the sum of the area of the six sides.
sa = (2 × l × w) + (2 × l × h) + (2 × w × h)
sa = (2 × 12 × 4) + (2 × 12 × 3) + (2 × 4 × 3)
sa = 96 + 72 + 24
sa = 192
The surface area is 192 m²