[monolithed]

<script type="text/javascript">
window.onload = function(){
	var count = 0;
	document.getElementById("check").onchange = function(){
		document.getElementById("input").value = (this.checked) ? count+=150 : count-=150;
	};
};
</script>

<input type="checkbox" id="check" value="" />
<input type="text" id="input" value="0" />