Answer:
Colin gets twice as much as Dan
Colin = Dan * 2
Dan gets three times as much as David
Dan = David * 3
Put this is terms of a ratio.
Colin:Dan:David
6:3:1
6 + 3 + 1 = 10
320 / 10 = 32
David = 32 * 1 = £32
Dan = 32 * 3 = £96
Colin = 32 * 6 = 96 * 2 = £192