Question 1118004
(a) and (b) do not seem to fit this kind of problem.

y, Harry
x, Hermione
r, Ron

{{{system(y=r/3,y=x-8,y=8)}}}


Substitute for y.
{{{system(8=r/3,8=x-8)}}}

{{{system(r=24,x=16)}}};


Sum of their ages:
{{{8+16+24}}}
{{{highlight(48)}}}