Question 1144129
<pre>
John             x+3
Sister           x
Mother           x+29
Father           x+33
Average M&F      (2x+29+33)/2
John+x           2x+3
</pre>
Other ways to follow the description into expressions are possible.  Here, just one variable is used, x for the sister.


{{{(2x+62)/2=2x+3}}}
Solve.