29) A

Total Area of 1 narrow wall = 4 x 2.5 = 10m²
Area of narrow wall with door = 10 – (1 x 2) = 8m²
Area of narrow wall with window = 10 – (2 x 1.5) = 7m²
Total Area of narrow walls = 8 + 7 = 15m²

1 tin paints 15m²
If person paints with high quality paint, two coats are needed = 15 x 2 = 30m²
Cost for 1 coat which is 15m² = £15
Cost for 2 coats of 15m² each = 15 x 2 = £30

If person paints with budget paint, three coats are needed = 15 x 3 = 45m²
Cost of three coats = 11 x 3 = £33
So the person should use quality paint for these walls.

Area of a wide wall = 5 x 2.5 = 12.5 m²
Total area of wide walls = 12.5 x 2 = 25m²

If person paints with high quality paint, two coats are needed = 25 x 2 = 50m²
Since 25m² is larger than 15m², the person would have to buy 2 tins (30m²) for 1st coat.
Cost of 2 tins = 15 x 2 = £30
5m² of paint would be left over. The person still needs to paint 25m² . Using the 5m² which is left over, there would be 20m² left. The person would still need to buy 2 more tins.
Cost for 2 more tins = 15 x 2 = 30
Total cost = 30 + 30 = £60

If person paints with budget quality paint, three coats are needed = 25 x 3 = 75m²
Since 25m² is larger than 15m², the person would have to buy 2 tins (30m²) for 1st coat.
Cost of 2 tins = 11 x 2 = £22
5m² of paint would be left over. The person still needs to paint 50m² . Using the 5m² which is left over, there would be 45m² left. The person would still need to buy 3 more tins.
Cost for 3 more tins = 11 x 3 = 33
Total cost = 22 + 33 = £55

To paint the wider walls, the person should opt for the budget paint.
Total cost = 30 + 55 = £85