## Precalculus (6th Edition) Blitzer

a. $y-24.6=0.12(x-10)$ or $y-25.8=0.12(x-20)$ b. $f(x) =0.12x+23.4$ c. $28.2$ per cent.
a. Use the given coordinates $(10,24.6)$ and $(20,25.8)$, we can calculate the slope as $m=\frac{25.8-24.6}{20-10}=0.12$. Thus, we can write the line equation in point-slope form as $y-24.6=0.12(x-10)$ or $y-25.8=0.12(x-20)$ b. We can rewrite the above equations in slope-intercept form as $f(x)=y(x)=0.12x+23.4$ c. For 2020, we have $x=2020-1980=40$ and $y(40)=0.12(40)+23.4=28.2$ percent.