The function represents the distance when he uses g gallons on a highway.
The given function is:
![D(g)=30g](https://img.qammunity.org/2023/formulas/mathematics/high-school/elghbov8zsiqubvf68oivj83dmbpnu7mjn.png)
If we want to find how far does all drives if he uses 4 gallons of gas, we need to replace g=4.
Then:
![\begin{gathered} D(4)=30(4) \\ D(4)=120 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/v4t5g3b75jare5vjwz8ypcini0og22coom.png)
Hence, he will be 120 miles away if he uses 4 gallons of gas.