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

8-21.

Find the equation of the line that passes through the points $\left(-800,200\right)$ and $\left(-400,300\right)$.

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 $b$.

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

$200 = −200 + b$

$400 = b$

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

Remember to check your work.

Use the eTool below to help find an equation that passes through these two points.
Click on the link at right for the full eTool version: 8-21 HW eTool (Desmos)