The Census Bureau most recent estimates of jobs by location is for 2017. In that year, they estimate there were 195,000 jobs in the city of Detroit. If Fiat Chrysler adds 4950 new jobs in the city, the total number of jobs in the city will go back to what it was before the start of the recession in 2008.
The Census Bureau estimated that, in 2017, there were about 50,000 Detroit residents who worked in the city. That will go up by 8% if
Fiat Chrysler hires 4100 Detroit residents. Of course, some of them may move to the suburbs if their income goes up substantially.

We still have a situation in which 74% of the jobs in the city of Detroit
are filled by suburban residents while 71% of the residents of the city who are employed work in the suburbs.