14) B

The key to answering this question is remembering that making a new colour requires equal amounts of other colours.

Brown requires equal quantities of red, yellow and green. Since the mural contains 30% brown, it must have 10% red, 10% yellow and 10% green. (equal amounts of all three colours make brown)

Green requires equal amount of blue and yellow. So there is 5% blue and 5% yellow extra. So far there is, 10% red, 15% yellow and 5% blue.

The mural also contains 20% red. Adding the initial 10% red in brown, there is a total of 30% red so far.

10% of blue
10% of yellow
10% of orange = 5% red and 5% yellow
10% of purple = 5% blue and 5% red
10% off green = 5% yellow and 5% blue

In total the mural contains:
Red = 10 + 20 + 5 + 5 = 40%
Yellow = 15 + 10 + 5 + 5 = 35%
Blue = 5 + 10 + 5 + 5 = 25%

Since 20ml of red is left, 80ml was used (there was initially 100ml of each colour).

40% = 80ml
1% = (80÷40) = 2ml
100% = 2 x 100 = 200ml
The mural contains 200ml of total colours.

Since the mural has 25% blue, amount of blue = 0.25 x 200 = 50ml