1. Let's start with a basic Grade 10 Indonesian mathematics topic: solving linear equations. 2. Problem: Solve the equation $3x + 5 = 20$ for $x$. 3. Formula and rules: To solve for $x$, we need to isolate $x$ on one side of the equation by performing inverse operations. 4. Step 1: Subtract 5 from both sides: $$3x + 5 - 5 = 20 - 5$$ $$3x = 15$$ 5. Step 2: Divide both sides by 3 to solve for $x$: $$\frac{3x}{\cancel{3}} = \frac{15}{\cancel{3}}$$ $$x = 5$$ 6. Explanation: We first removed the constant term 5 by subtracting it from both sides, then divided both sides by the coefficient of $x$, which is 3, to isolate $x$. 7. Final answer: $x = 5$. This is a fundamental skill in algebra that will help you solve many types of equations.