It is a because each day you run 5 miles, meaning 100 miles is decreasing since you keep running the miles away, for example if you ran for 4 days 100-20, because we multiplied 4x 5( the amount of miles) and now we would have 80 miles to go
The second option is not correct because you are not adding more than what her goal is.
The third option is not correct because you are not dividing from her goal.
The fourth option is not correct because it would ultimately result in a negative number.
The first option is correct because it subtracts how many days she has ran times 5 from her goal. The resulting answer would show how many miles she has left to reach her goal of 100 miles during that month.
