A tank is 25 m long, 12 m wide, and 6 m deep. Find the total cost of plastering its four inner walls and the bottom at the rate of 75 paise per square metre (₹0.75 per m^2).

Introduction / Context:
This question tests surface area calculation of a cuboid-like tank and cost computation. Plastering the tank's inner walls and bottom means we include the area of the four side faces plus the bottom face, but not the top (open surface). Then multiply the total area by the cost rate per square metre.

Given Data / Assumptions:

• Length l = 25 m
• Width w = 12 m
• Depth/height h = 6 m
• Rate = 75 paise per m^2 = ₹0.75 per m^2
• Plastering includes: 4 walls + bottom (no top)

Concept / Approach:
Area of four walls = perimeter of base * height = 2(l + w) * h. Bottom area = l*w. Total plaster area = 2(l + w)h + l*w. Cost = total area * rate.

Step-by-Step Solution:
Area of four walls = 2(l + w) * h = 2(25 + 12) * 6 = 2*37*6 = 444 m^2 Bottom area = l*w = 25*12 = 300 m^2 Total area = 444 + 300 = 744 m^2 Cost = 744 * 0.75 = ₹558

Verification / Alternative check:
If you compute each wall separately: two walls are 25*6 each and two are 12*6 each, total walls = 2*150 + 2*72 = 300 + 144 = 444 m^2. Adding bottom 300 gives 744 m^2, consistent.

Why Other Options Are Wrong:
₹258 and ₹358: correspond to much smaller plaster area or a missing face in calculation. ₹458: could happen if someone forgets to include the bottom or uses wrong height. ₹608: would imply a total area around 810+ m^2 at ₹0.75, which is not correct here.

Common Pitfalls:
Including the top surface even though a tank is typically open at the top. Forgetting to add the bottom area. Using 75 as rupees instead of 75 paise (₹0.75).

Final Answer:
Total plastering cost = ₹558