Hi Lauren, thanks for asking your question. I'll try to explain these problems that are on the chapter 2 test.

#15 & 17 on the test do not have decimals to deal with. #18 & 19 do have decimals, but only in such a way as should be known previous to starting this course. One of the prerequisites for beginning algebra is to already know how to add, subtract, multiply, and divide decimals.

For #15, you are trying to figure out a formula based on the table of the function that is given. What patterns do you notice? Use the table to see if you can write a math expression for how using the x value, the function is getting the y value.

#17, you are using the formula for a function that is given to create a table. Then you will use the table to graph the function. The table shows coordinate points for the graph.

#19, you are using the formula given for the ball to finish the table that is there. If x = 20, what will y equal for the function with the formula y=0.8x.

The linear functions in chapter 2 do follow a slope-intercept form, but slope and y-intercepts have not been covered in this course yet. They will be covered in a later chapter. So, those are something to look forward to. :)
For this chapter, the main focus is functions. So, to graph these functions you will need to create or already be given a table for the functions in order to have coordinate points to plot. Does that make sense?

Let me know if you have any other questions I can help with!