Answer:
A. 100 - 5d
Step-by-step explanation:
When d=0, Rosa has 100 miles remaining. That fact eliminates choices C and D, which do not give the value 100 when d=0.
After Rosa runs 1 day, she has 95 miles remaining. That eliminates choice B, which tells you she has 105 miles remaining.
The only viable choice is A.
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You could write this expression yourself by realizing that Rosa starts with 100 miles remaining and decreases that amount by 5 each time the value of d increases by 1. That is, the expression 5d represents the number of miles Rosa runs in d days. This number is subtracted from her goal to give the remaining miles, so 100-5d is the number she has remaining of her goal.
