Question

It takes 1.5 litres of sugar soap to wash a square meter of ceiling and 0.5 litres of sugar soap to wash a square meter of wall. Bianca's room is 4 metres high and each wall is 5 metres wide. There is one window, which is 4 square metre and a door, which is 9 square meter. How much sugar soap will Bianca need, assuming she does not wash the door or window has ( a room has four walls and a roof)?

Answer 1

I gave it a try
for an easier way of understanding.... try to visuallise Bianca's room as a cuboid.
length=5
breadth=5
height=4
area of the ceiling=5x5=25 square metre
area of total room= no. of faces in a cubiod x 25
                            = 6 x 25
                            = 150
area of four walls= [excluding ceiling and floor (2 faces excluded)]
(25x2=ceiling and floor) = 150 - (25 x 2)
                                       =150 - 50
                                       =100
litres of sugar soap needed for ceiling = 25 x 1.5 = 37.5
litres of sugar soap needed for walls = 100 x 0.5 = 50
total no. of litres needed for Bianca's room = 37.5 + 50 =87.5

Ans: Bianca will need 87.5 litres of sugar soap.

Answer 2

Area of ceiling is 5x5 =25 m²
so sugar soap required = 25x1.5 =37.5 Litres
now the walls 
area of 4 walls = 4(4x5) =80 m²
area to be washed = 80 -(9 +4) = 80 - 13 = 67 m²
sugar soap needed = 67x 0.5 = 33.5 Litres
total volume = 37.5 + 33.5 = 71 Litres