For this case we have:
- Operating costs = $ 680 per day
Part A:
Since d is the variable that represents the number of days, we can represent an inequality for the gains given by:
![680d + 52000 <960d\\](https://img.qammunity.org/2019/formulas/mathematics/high-school/s9uczhpu0z3z26lbq42kf35q63ylsd9spt.png)
Part B:
We want to know the moment from which Julianne obtains earnings, for that we clear d of the previous inequality:
![52000 <960d-680d\\\\52000 <280d\\\\(52000)/(280)<d\\](https://img.qammunity.org/2019/formulas/mathematics/high-school/h67wfd2n9yyau0id4hsy3yfzxrvkc1lhyw.png)
![185.7 <d\\\\d> 186 days\\](https://img.qammunity.org/2019/formulas/mathematics/high-school/vukfk2jnfpkn9iqm6j6md6ac51md0x8501.png)
To start making a profit, Julianne must work more than 186 days.
Answer:
![680d + 52000 <960d\\\\d> 186 days\\\\](https://img.qammunity.org/2019/formulas/mathematics/high-school/xlcorut2c246icvulmlq7qwesfo6snh4nh.png)