External height (l) of book self = 85 cm
External breadth (b) of book self = 25 cm
External height (h) of book self = 110 cm
Externalsurface area of shelf while leaving out the front face of the shelf
= lh +2 (lb + bh)
= [85 × 110 + 2 (85 × 25 + 25 × 110)] cm2
= (9350 + 9750) cm2
= 19100 cm2
Area of front face = [85 × 110 − 75 × 100 + 2 (75 × 5)] cm2
= 1850 + 750 cm2
= 2600 cm2
Area to be polished = (19100 + 2600) cm2 = 21700 cm2
Cost of polishing 1 cm2 area= Rs 0.20
Cost of polishing 21700 cm2 areaRs (21700 × 0.20) = Rs 4340
It can be observed that length (l),breadth (b),and height (h)of each row of the book shelf is 75 cm, 20 cm, and 30 cm respectively.
Area to be painted in 1 row = 2 (l + h) b + lh
= [2 (75 + 30) × 20 + 75 × 30] cm2
= (4200 + 2250) cm2
= 6450 cm2
Area to be painted in 3 rows = (3 × 6450) cm2 = 19350 cm2
Cost of painting 1 cm2 area= Rs 0.10
Cost of painting 19350 cm2 area= Rs (19350 × 0.1)
= Rs 1935
Totalexpense required for polishing and painting = Rs (4340 + 1935)
= Rs 6275
Therefore, it will cost Rs 6275 for polishing and paintingthe surface of the bookshelf.