i need help with rate of change on a linear graph please

Using the points (2014,22320) and (2020,0), we get the following slope:
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ \Rightarrow m=\frac{0-22320}{2020-2014}=\frac{-22320}{6}=-3720 \\ m=-3720 \end{gathered}[/tex]now we use the point (2020,0) to find the relation function:
[tex]\begin{gathered} y-y_0=m(x-x_0) \\ \Rightarrow y-0=-3720(x-2020) \\ y=-3720(x-2020) \end{gathered}[/tex]to find the missing values, we substitute each one in x and see the result of y:
[tex]\begin{gathered} x=2015 \\ \Rightarrow y=-3720(2015-2020)=-3720(-5)=18600 \\ x=2017 \\ \Rightarrow y=-3720(2017-2020)=-3720(-3)=11160 \end{gathered}[/tex]therefore, in 2015 the debt was $18600 and in 2017 it was of $11160.
For year 2014 we have the total ($22320) and in 2020 we have that the debt is $0