Question 1069154
s, son
d, daugher


The description as a system of equations:
{{{system(d=3s,s+10+d+10+42+10=100)}}}



{{{s+d=100-42-30}}}
{{{s+d=28}}}
substitute for d;
{{{s+3s=28}}}
{{{highlight(s=7)}}}
-
{{{highlight(d=21)}}}