1) C

Amount of yellow paint used = 1500 – 900 = 600 ml

Yellow is only used in making orange paint. Equal amounts of red and yellow is used to make orange.

So amount of red used in making orange = 600 ml
Total amount of orange paint made = 600 + 600 = 1200 ml

Since he made exactly the amount of paint that he needed, he used 1200 ml of orange paint.
40% = 1200
1% = 1200/40 = 30 ml
Hugh painted the room 60% pink
60% = 30 x 60 = 1800 ml

Ratio of red and white paint = 1 : 3
Total parts = 1 + 3 = 4
Amount of red paint used to make pink paint = 1800 / 4 = 450 ml
Total red paint used = 600 + 450 = 1050 ml
Total red paint left = 1500 – 1050 = 450 ml