The function represents the distance when he uses g gallons on a highway.
The given function is:
[tex]D(g)=30g[/tex]If we want to find how far does all drives if he uses 4 gallons of gas, we need to replace g=4.
Then:
[tex]\begin{gathered} D(4)=30(4) \\ D(4)=120 \end{gathered}[/tex]Hence, he will be 120 miles away if he uses 4 gallons of gas.