After 3 hours, you will be on 450 mile marker.
Step-by-step explanation:
step 1: At start, the number in the mile marker is 100
step 2: After 4 hours, the number in the mile marker is 300
step 3: The difference of 300-100= 200. In 4 hours you crossed 200 mile markers.
step 4: Therefore, for 1 hour you can cross= 200/4= 50 mile markers.
For 3 hours, the number of mile markers crossed= 3*50= 150 mile markers.
step 5: After 3 hours, the number in the mile marker will be= 300+150= 450
