Units started and completed (Process Costing)

A company which operates a process costing system had work-in-progress at the start of last month of 300 units (valued at $1,710) which were 60% complete in respect of all costs. Last month a total of 2,000 units were completed and transferred to the finished goods warehouse. The cost per equivalent unit for costs arising last month was $10. The company uses the FIFO method of cost allocation.
What was the total value of the 2,000 units transferred to the finished goods warehouse last month?
A $19,910
B $20,000
C $20,510
D $21,710

Hello. I know the answer for the question is A and the units started and completed is 1700 however it’s kind of confusing me since the same logic doesn’t seem to be applying to the question below:

The following Information relates to process 3 of a 3-stage production process for the month of January 20X4.

Opening Inventory
300 units complete as to:
Materials from Process 2 100% $4400
Added materials 90% $1150
Labour 80% $540
Production overhead 80% $810

In January 20X4, a further 1800 units were transferred from process 2 at a valuation of $27000. Added materials amounted to $6600 and direct labor to $3270. Production overhead is absorbed at the rate of 150% of direct labor cost. Closing inventory at 31, January 20X4 amounted to 450 units, complete as you:

Process 2 materials 100
Added materials 60%
Labour and overhead 50%

DR
Opening WIP 300units $6900
Input from P2 1800units $27000
Added materials 6600
Direct Labour 3270
Production Overhead 4905

CR
Opening WIP to to completed 300units $7320
+
Units started and completed 1350units $32400
=
Output 1650units $39720
Closing WIP 450units $8955

Does someone has a clear formula for finding units started and completed? Usually I just do Input-Closing WIP but that doesn’t seem to be working in the first example.