Expected throughput is
1000 units/h
Therefore the expected time for 4800 units is
(4800 units)/(1000 units/h) = 4.8 hours = 288 minutes
Because the worker is 48 minutes behind schedule, the actual time is
288 + 48 = 336 minutes = 5.6 hours
The actual average throughput is
(4800 units)/(5. h) = 857 units per hour.
Answer: 857 units per hour.