I am a beginner with PHP and I would like to know how can I get the parts `x`, `y`, `z`, and `t` of a sequence of characters which has the form `"x, y, z, t"`:

Example: 

```
$str1 = "2,161,0,0"; 
$str2 = "2,3,10,4";

```

for `$str1` we have to recover:

```
2 -> x

161 -> y

0 -> z

0 -> t

```