Answer:
120 ft
Step-by-step explanation:
A slope of 12/100 means for every 12 units of distance you move horizontally you descend by 100 of the same units vertically. Assuming now that the slope does not change, i.e it remains constant throughout your trip; descending by 1000 ft should mean you have moved horizontally by 120 ft so that the slope is maintained.
x/1000 = 12/100
x = 120 ft