Learning curve

Question: A business has developed a new product. The first batch of 50 units takes 750 labour hours to produce. There will be an 90% learning curve that will continue until 3550 units have been produced. Batches after this level will each take the same amount of time as the 71st batch. The batch size is 50 units.
Note. The learning index for a 90% learning curve is -0.152. Ignore the time value of money.
What is the time taken for the 71st batch?
392.35 hours
330.75 hours
393.23 hours
345.65 hours

I calculated the answer to be 333.06807 hours, but this does not match any of the options listed. So is my answer incorrect, or is it due to the rounding difference. And if it is due to the rounding, then what should I do in the exam. Here I took the full calculator value when calculating the average time per batch for 70 batches and 71 batches, and the total time for 70 and 71 batches, but at the back of the book the average time per batch for 70 and 71 batches has been calculated only to four decimal places whereas the total time for 70 and 71 batches has been calculated to two decimal places. So which is correct? Should I take the full calculator value or calculate the average time to four decimal places and total time to two decimal places. Here I used the full calculator value and calculated the answer, but it does not match any of the options, and I don’t understand why.