Textbook Topics: Formulas Part I (Algebra)

Chapter 2 of my textbook is all about formulas and equations in the context of algebra, however Exercise 2.03 specifically focuses on formulas.
The textbook defines formulas as “an algebraic rule that describes a mathematical relationship between variables.”
I’ve always loved formulas as I believe having a formula to follow is the easiest way to solve a mathematical problem I’m presented with. It’s just a matter of making sure I apply the correct number to the correct variable, “filling the gaps” if you will.
When I reached Exercise 2.06 – Changing the subject of a formula, I found this topic interesting but also a challenge to implement. The textbook states that to change the subject of a formula to another variable, “use the same rules as for solving an equation. The answer is not a number but an algebraic expression (another formula).”
I found it interesting that the subject of a formula could be changed but also a challenge as I would usually answer the questions incorrectly by making the wrong variable the subject of the formula, or I would have the variables in the wrong order, e.g. t = s/m when the answer should have been t = m/s.
Formulas aren’t just restricted to Chapter 2, it turns out they are present throughout the textbook.