Spinster Co (Learning curve, BPP revision kit)

The Background: Spinster Co has developed a new product. The first batch of 10 units will take 300 labour hours to produce. There
will be an 80% learning curve that will continue until 540 units have been produced. Batches after this level will
each take the same amount of time as the 54th batch. The batch size will always be 10 units.
Note: The learning index for an 80% learning curve is -0.3219
Ignore the time value of money.

The Question: The total time for the first 16 batches of units was 3,300 hours. What was the actual learning rate closest to
the nearest %?

Answer as per BPP revision kit:

Batch 1, Total time 300, Average time/unit, 300
Batch 2, Total time x, Average time/unit, 300 × r
Batch 4, Total time x, Average time/unit, 300 × r2
Batch 8, Total time x, Average time/unit, 300 × r3
Batch 16, Total time 3300, Average time/unit, 300 × r4

Working as per BPP revision kit:
3,300 = 16 × 300 r4
3,300/(16 × 300) = r4
r = 0.91 or 91%

Here I could not understand how the “3,300/(16 × 300)” is equal to 0.91. As per calculator, it should be equal to 0.69. Please help in clarifying. Thank you in advance!