Let's analyze the data provided in the table and address each part of the question:

a. Make a scatter plot of the data.

We will create a scatter plot with the Grade on the x-axis and Time (min) on the y-axis.

b. What are the coordinates of the point that represents the longest time spent on homework?

To find this, we look for the highest value in the "Time (min)" column.

From the table, the longest time spent is 80 minutes by an 8th grade student. So, the coordinates are: $(8, 80)$

c. Does a relationship exist between grade level and time spent studying? If so, write a sentence to describe the relationship. If not, explain why not.

To determine if there is a relationship, we need to examine the scatter plot or the data pattern.

Here is the data in tabular form:

Grade	Time (min)
2	20
2	15
2	20
4	30
4	20
4	25
4	40
4	30
6	60
6	45
6	55
6	60
8	70
8	80
8	75
8	60

From the scatter plot and the table, it appears that there is a general trend: as the grade level increases, the time spent studying also tends to increase.

Description of the Relationship

There seems to be a positive correlation between grade level and time spent studying. As students advance to higher grades, they tend to spend more time studying.

Would you like more details or have any questions?

Here are 5 questions you might want to ask:

1. 如何用回归分析来确定数据之间的关系？
2. 什么是散点图，如何解读散点图？
3. 如何计算数据集的平均值？
4. 如何判断两个变量之间是否存在相关性？
5. 如何计算数据的标准差？

Tip: 使用图表可以直观地展示数据之间的关系，帮助你更容易地发现趋势和模式。