<?php
// Using a session for recalling the number on a later page is probably
// the easiest solution.
session_start();
// Store the number in our session:
$_SESSION['number'] = $_POST['number'];
// Mutliply the number by a price
$object_price = 19.95;
$cost = $_SESSION['number'] * $object_price;
// I don't know what you're summing together, so here's
// some arbitrary number...
$sum = $_SESSION['number'] + 5;
// Basic math to find percent saved (to one decimal place)
$saved = number_format(($object_price - $cost) / $object_price, 1);
There's some basic examples... it wasn't very clear to me what you were summing together, or where the price came from, etc. etc. so you'll have to insert the appropriate information.