Explanation:
the ratio is 4:8:5 for Richard, Allan and Fliss.
the sequence is important.
the money pool between them has 4+8+5 = 17 equal units.
Richard has 4 units of these 17, Allan has 8 units, and Fliss has the remaining 5 units.
we don't know the value of such a unit yet.
this we get from the second hint :
Allan gets £9 more than Fliss.
remember, Allan has 8 units, Fliss 5.
so, Allan has 3 units more than Fliss.
that means these 3 units are worth £9.
and that means each unit is worth 9/3 = £3.
Richard has 4 units, that means he has
4×3 = £12