i would like to change the height of a div. i would like to do this in increments of 50 (each time the personclicks [+] for example). and same goes for subtracting height. unfortunately, the height var is '200px' when it's retrieved, and i cant add '200px' to '50' b/c it turns into '200px50' and thats not a valid height. :/

	function plusHeight(id) {
		var height = document.getElementById(id).style.height;
		height = height + '50';
		document.getElementById(id).style.height = height;