I have an array that I am using to display form dropdown options. I would like to be able to display the key of a specified array element. 

```
$options = array(
                    '10' => '10 Results',
                    '15' => '15 Results',
                    '20' => '20 Results',
                    '25' => '25 Results',
                    '30' => '30 Results'
                );

```

If I use 

```
$selected = '25';
echo $options[$selected]

```

this of course returns "25 Results". How would I return the key of that element? 

```
key($options)

```

The above would just return the key of the first element of the array.