Process costing

At the start of the month, there were 2,000 units of work-in-progress in a factory. During
the month, 12,000 units were started. At the end of the month, 3,000 units were in closing
work in progress. The degree of completion of opening work-in-progress was 70% and
closing work-in-progress was 20%.

How many equivalent units of production were achieved during the month if FIFO were
used?

my working:

Units started and finished = 12,000-2,000=10,000
Closing WIP 3,000 X 20% = 600
Opening WIP 2000 X 30% = 600

my answer = 10,000+600+600=11,200

I made only a mistake calculating “Units started and finished” and I don’t get it why.

their working:
Units started and finished=11,000-2000
Closing WIP 3,000 X 20% = 600
Opening WIP 2000 X 30% = 600
The answer = 10,200.

thanks in advance