This document discusses using What-If Analysis in Excel 2007 to determine unknown variables. It explains how to use the Goal Seek tool to find the interest rate needed for a $400 monthly car loan payment on a $20,000 loan over 5 years. The document provides step-by-step instructions for inserting the PMT function to calculate payments, accessing the Goal Seek tool, and setting it to determine the 7% interest rate that satisfies the goal of a $400 monthly payment. Users are challenged to practice this on the included Car Loan workbook.