7500 cars
a worker works 5*8=40 hours per week
1 week of time
each modification takes one worker 1h 15m=1,25h=(5/4)h
calculate how many modifications one worker can make in the 40 hours/one week
40/(5/4)=160/5 =32
calculate the necessary amount of workers
7500/32=234,375
->round up, because we can't assign parts of workers-> 235 workers are necessary to meet the deadline