Answer:
![(dy)/(dx)=8.5](https://img.qammunity.org/2021/formulas/mathematics/high-school/oh1a3fyse7irqur95qrl7z6idoghl0407x.png)
Explanation:
Let
denotes number of windows and
denotes the number of yards of fabric needed.
Stephen is making curtains for several windows in his aunt's house. He determines that he needs 8.5 yards of fabric for each window.
a. Equation becomes
![y=8.5x](https://img.qammunity.org/2021/formulas/mathematics/high-school/fjud4s9i0wsq8pow5zuxwa98it703oedtk.png)
This answer is already given in question.
b. To find rate of change in this situation, find
![(dy)/(dx)](https://img.qammunity.org/2021/formulas/mathematics/high-school/uixpzcj18ltl0o4d3t4rqypg7shavk8rb9.png)
![y=8.5x](https://img.qammunity.org/2021/formulas/mathematics/high-school/fjud4s9i0wsq8pow5zuxwa98it703oedtk.png)
Differentiate with respect to
![x](https://img.qammunity.org/2021/formulas/mathematics/middle-school/p9sq9b3rc5nwoqzhzc8wcaj51b36281l9g.png)
![(dy)/(dx)=8.5(1)=8.5](https://img.qammunity.org/2021/formulas/mathematics/high-school/41o6g8izv7fjfb6ozf3tuu71ty46vl9kq3.png)