Question 822831
I took out the rendering braces so we can read the description and question with much less trouble.


Using p as parker
q as quinn
k as Karl


q=2k;
q=4+p;
p+q+k=21.


Substitute for q in the age sum equation; and equate the right members of the first two equations, so you'll have two equations in just p and k.
p+(2k)+k=21 and 2k=4+p;
p+3k=21 and 2k=p+4;
p+3k=21 and p-2k=-4.
Now, with these two equations, if you will subtract one of them from the other, you can quickly get a value for k.  Elimination method, eliminating p.
You obtain 5k=25,
{{{highlight(k=5)}}}.


Now you can go back to the first equation for q;
q=2k
q=2*5
{{{highlight(q=10)}}}


Using second original equation,
q=4+p
10=4+p
{{{highlight(p=6)}}}