How do you get to 375 shifts ?
We need to produce 290.000 untis.
We can produce 800 units per 12 hour shift.
290.000/800=362,5 shifts

I get that 300.000 / 800 = 375 shifts.

So is the exervise solution wrong ?

“20 employees needed to produce 800 units. ” The 20 employees are not mentioned in the solution. I think you have to multiply the day and night shift hours by 20, because 20 peolpe are working one shift and each of them earn 15$/20$. Thats how I interpreted this.

I also recomend to define what a day and night shift is in the exercise.