Let's break down the given information and the function to fully understand what each part represents.
1. **What does \( t \) represent?**
\( t \) represents the time in minutes since the balloon started descending.
2. **What does \( a(t) \) represent?**
\( a(t) \) represents the altitude of the hot air balloon (in presumably feet or meters) at time \( t \) minutes after the descent starts.
3. **What information will \( a(5.5) \) give?**
\( a(5.5) \) will give the altitude of the hot air balloon 5.5 minutes after it started descending.
To find \( a(5.5) \):
\[
a(5.5) = 210 - 15 \cdot 5.5
\]
\[
a(5.5) = 210 - 82.5
\]
\[
a(5.5) = 127.5
\]
So, \( a(5.5) \) gives the information that the altitude of the balloon is 127.5 units (e.g., feet or meters) 5.5 minutes after it started descending.