1. The problem asks us to write an equation for the thickness of a pipe wall as a function of its age in years. 2. We know the initial thickness is 2.25 cm, and it decreases by 0.3 cm each year. 3. The general form for a linear function is $$y = mx + b$$ where: - $y$ is the thickness after $x$ years, - $m$ is the rate of change (slope), - $b$ is the initial value (thickness at $x=0$). 4. Here, the slope $m = -0.3$ cm/year (since thickness shrinks), and the initial thickness $b = 2.25$ cm. 5. Substitute these values into the formula: $$y = -0.3x + 2.25$$ 6. This equation means for each year $x$, the thickness $y$ decreases by 0.3 cm from the initial 2.25 cm. 7. To check, at $x=0$ years, $y = 2.25$ cm, and at $x=1$ year, $y = 2.25 - 0.3 = 1.95$ cm. Thus, the equation representing the thickness as a function of age is: $$\boxed{y = -0.3x + 2.25}$$