Answer
Brianna: $-0.05$
Meilin's: $-0.08$
Work Step by Step
We use the staring and ending points on the graph to find the slope (rise over run):
The rate of change/grade of Brianna's road is:
$\frac{f(y)-f(x)}{y-x}=\frac{0-500}{10000-0}=-0.05$ or $-5\%$.
The rate of change/grade of Meilin's road is:
$\frac{f(y)-f(x)}{y-x}=\frac{0-1200}{15000-0}=-0.08$ or $-8\%$.
