They already cover 20 mi and every hour they advance 50mi, so if we call f(x) as the distance and x as the time in hours the function will be:
[tex]f(x)=50x+20[/tex]
The mimimun value for x has to be 0 because when x = 0, f(x) is equal to 20 that is the initial position.
and fot the maximun values of x will be when f(x) = 120
[tex]120=50x+20[/tex]
and we solve for x
[tex]\begin{gathered} 120-20=50x \\ 100=50x \\ \frac{100}{50}=x \\ 2=x \end{gathered}[/tex]
so the domain will be:
[tex]0\le x\le2[/tex]
