shell scripting

How would I write a script for  the scriptfile "puzzlescript"  to make the gotchascript echo back "gotcha" ?  The idea here is to set up the first script named gotcha so that when $sum and $rightsum are equal the script will echo back gotcha.  It is set up to look at and execute the scriptfile 'puzzlescript'  to see if its value is equal to $rightsum.  Puzzlescript is set up in another part of the directory and has to be written in such a way that when the gotchascript comes to run it, it triggers the echo gotcha from the gotchascript.

#!/bin/bash
#gotchascript

if [ ~/puzzle ]
then
sum=` ~/puzzle 5 10 20 $$`
rightsum=`expr 35 + $$`
if [ $sum -eq $rightsum ]
then
echo gotcha
echo
fi

What I've come up with so far is,

#!/bin/bash
#puzzlescript

sum=`expr 5 + 10 + 20 + $$`
echo $sum

but it won't cause the echo gotcha from the gotchascript