### Home > AC > Chapter 8 > Lesson 8.1.2 > Problem8-21

8-21.

Find the equation of the line that passes through the points $(−800{,}200)$ and $(−400{,}300)$.

Find the growth.

$\text{Slope (growth) }=\frac{\text{change in }y}{\text{change in }x}=\frac{100}{400}$

$\textit{m}=\frac{1}{4}$

Substitute the growth ($m$) and a point $(x, y)$ from the problem into $y = mx + b$. Solve for $b$.

$200=\frac{1}{4}(-800)+\textit{b}$

$200 = −200 + b$

$400 = b$

$\textit{y}=\frac{1}{4}\textit{x}+400$