You can use a RegExp to match the string or use String subString to extract the "-205".

The end result is you need to convert this value to an integer and divide this value by 10 and display using toFixed(1).

var textThatHasBeenExtracted = "-205";
var int = parseInt(text,10).toFixed(1);

This is where you need to find a good RegExp and JavaScript reference such as W3Schools.