70 shirts per day
We simply need to find how many shirts would have been produced on the 8th day. This can be done by multiplying the number of extra shirts produced per day by the number of days extra shirts were produced. Since one day was skipped due to finishing early, there were 7 days of producing extra shirts.
7 times 10 equals 70. This means that 70 shirts would have been produced on the 8th day, which means the factory was planning on producing 70 shirts for every other day as well.