For this case we have:
Part A:
Since d is the variable that represents the number of days, we can represent an inequality for the gains given by:
[tex]680d + 52000 <960d\\[/tex]
Part B:
We want to know the moment from which Julianne obtains earnings, for that we clear d of the previous inequality:
[tex]52000 <960d-680d\\\\52000 <280d\\\\\frac{52000}{280}<d\\[/tex]
[tex]185.7 <d\\\\d> 186 days\\[/tex]
To start making a profit, Julianne must work more than 186 days.
Answer:
[tex]680d + 52000 <960d\\\\d> 186 days\\\\[/tex]