Part A:
For this case, the rate of change is given by the slope of the straight line.
We have then:
![m= (y2-y1)/(x2-x1)](https://img.qammunity.org/2019/formulas/mathematics/high-school/t7s96avj3819wajdbsr1oelo1nhv9ycg02.png)
Substituting values we have:
![m= (0-150)/(5-0)](https://img.qammunity.org/2019/formulas/mathematics/high-school/f2ayvurngk72fl3yivwjlajsv4s8qalbn0.png)
Rewriting:
![m=-30](https://img.qammunity.org/2019/formulas/mathematics/high-school/ypcctas29xnj0r84aqlt277or77rpc7cv1.png)
On the other hand, the initial value of the function occurs when x = 0.
We then have that for x = 0 the value of the function is 150.
Therefore we have:
Answer: m=-30, b = 150 The slope of the line represents the number of songs downloaded per week.
The cut-off point with the y-axis represents the initial number of songs that must be downloaded
Part B:
For this case the generic equation of the line is given by:
![y = mx + b](https://img.qammunity.org/2019/formulas/mathematics/high-school/i6zw0h9pe9ud2am0fso5etqxn9ng1dt2x4.png)
Where,
m: slope of the line
b: cutting point with the y axis.
Substituting the values of the part we have:
Answer: An equation in slope-intercept form to model the relationship between x and y is:
![y=-30x+150](https://img.qammunity.org/2019/formulas/mathematics/high-school/5rk905rgximzwu56yjow7ukjnvmo4k7mkg.png)