$(document).ready( function() {
	
	var priceElem = $('#final_order span');
	var baseSum = 110;
	var regex = /(\d+)/;
	var result = regex.exec( priceElem.html() );
	if( result ) {
		$('#numPages').change( function() {
			var finalSum = baseSum + ( $(this).val() - 1 )*0.5*baseSum;
			var newSum = priceElem.html().replace( regex, finalSum );
			priceElem.html( newSum );
		})
	}
})