How do I pass a variable from one function to another?

Say I have code that looks like this:

[code=php]
$a = 5;

function test($a) {
$b = $a+5;
return $b;
}

//How do I get $b to come out of the function?

function test($b) {
$c = $b+5;
return $c;
}

echo(test2($b));[/code]

The resulting answer is 5 when it should be 15, so my variable is not coming out of the first function – how do I fix this? Thanks in advance.

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