This essays is about 4441 Most Useful and Common Rules in Mathematical Financial Laws. So then Financial Engineer could always optimizing the Public Firm's Financial Measures in any condition, after making optimum decision based on the desired state of arts and known facts, at its best composition. Like many engineers know, a proper complex construction is much more difficult than just a simple new idea. It must deal with thousands of conflicting criteria, that must be computed and prioritized to produce its excellent financial structures. The nicest thing about it, is that only requires simple Junior Highschool Algebra. We just need to be consistent with its less number treatment of constellations. Its saddest part is that many professors and doctors are no longer able to understand Junior Highschool Algebra, and hiding in Accounting jargons. We try very hard to make this book as numerical as possible, with common T-Accounts of Balance Sheet and Income Statement, but we must deliver so many materials in this limited book pages, suitable to be brought traveling anywhere. Please go back to its Introduction for glossary, at anywhere inside the book, so then we can still understand what are those mean with simple Algebraic Rule there. We try to avoid some sentences multiplied, added, eliminated divided, rooted or powered by another sentences, that make many traditional finance book successful (delivering few simple things, seen as difficult and scary), but less useful and seldom be accurate.