Strange description.
If "Bill is 5 times older than Keira, Bill is 5 times older than Phil,", then Keira and Phil are the same age.
Bill k+5k=p+5p
Keira k
Phil p
Oscar 2(k+5k)=2(p+5p)
TOTAL 81
That table can be simplified because the simple addition and k=p.
Bill 6p
Keira p
Phil p
Oscar 12p
TOTAL 81
Question asked essentially for p.