A rectangular pit 8 m long, 5 m wide and 2 m deep is dug for a foundation. Digging costs ₹35 per cubic metre. Find the total cost.

A cuboid has 3 pairs of identical opposite faces. Their total area:

- 2 faces of $l\times b$ (top + bottom)
- 2 faces of $b\times h$ (front + back)
- 2 faces of $l\times h$ (left + right)

**TSA of cuboid = $2(lb+bh+hl)$.**
**LSA of cuboid = $2h(l+b)$** — only the four side walls, used for room painting (not floor/ceiling).

Special case (cube, $l=b=h=s$): TSA = $6s^2$, LSA = $4s^2$.