1. The problem is to solve a math question suitable for a senior five student in Rwanda. Since the user did not specify a particular problem, I will demonstrate solving a common algebra problem: solving a linear equation. 2. Let's solve the equation $3x + 5 = 20$. 3. The formula used here is to isolate the variable $x$ by performing inverse operations. 4. Step 1: Subtract 5 from both sides to get rid of the constant term on the left. $$3x + 5 - 5 = 20 - 5$$ $$3x = 15$$ 5. Step 2: Divide both sides by 3 to solve for $x$. $$\frac{\cancel{3}x}{\cancel{3}} = \frac{15}{3}$$ $$x = 5$$ 6. Therefore, the solution to the equation $3x + 5 = 20$ is $x = 5$. This method can be applied to any linear equation by isolating the variable step by step.