The graph shows the height of a hot air balloon over time as it descends. The vertical axis represents the height $h$ in meters, and the horizontal axis represents time $t$ in minutes.

To determine how high the balloon was when it began its descent, we need to find the height at time $t = 0$, which is the y-intercept of the graph.

From the graph, when $t = 0$, the height $h$ is 90 meters. Therefore, the balloon was 90 meters high when it began its descent.

Would you like further explanation on any part of this or have any other questions?

Here are some related questions:

1. How long did it take the balloon to descend to the ground?
2. What is the rate of descent of the balloon (slope of the graph)?
3. How can you model this situation with a linear equation?
4. How would the graph change if the balloon descended at a slower rate?
5. How does the height of the balloon change with respect to time?

Tip: The y-intercept of a graph represents the initial value in a real-world situation, like the starting height of the balloon here.