octal and hexadecimal values in php

For calculating octal numbers the formula is
$a=010

$a=1x8^1+0x8^0=8

For hexadecimal values

$b=0xA

$b=10

Here A=10,...,F=15.

Question :
What is the output of the following?


$a = 010;
$b = 0xA;
$c = 2;

print $a + $b + $c;

?>

Answer:

1. 20
2. 22
3. 18
4. $a is an invalid value
5. 2
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