Let the cost of a shirt be s.
Three shirts = 3s.
3s + 15 ≤ 80 (Answer F)
Did you ever get the answer?
Answer: Interval = [103,∞)
Explanation :
A medicine become ineffective if its temperature ever reaches 103 degrees Fahrenheit or more .
So, Interval becomes [103,∞)
i.e. semi-open or semi-closed interval as it includes 
So, we used closed brackets i.e. square brackets and
For '∞' we always use open brackets only.