Surface area is the total amount of space covering the outside of a 3D object.
Think of it like wrapping a present 🎁. The amount of wrapping paper you need to cover the entire box is its surface area.
👉 Surface area = add up the areas of all the outside faces/surfaces.

Top: 12 x 3 =36
Bottom: 12 x 3 = 36
left side: 7 x 3 = 21
right sde: 7 x 3 = 21
front: 12 x 7 = 84
back 12 x 7 = 84
36 + 36 + 21 + 21 + 84 + 84 = 282 cm2