Put 8 into fraction form: 8/1
Put 1 2/5 into a mixed number: 1*5+2 as numerator and 5 as denominator (7/5)
Now multiply 8/1 by the reciprocal of 7/5, which is basically just the numerator and denominator flipped, so 5/7. This is like dividing.
8/1*5/7= 40/7
40/7= about 5.7.
So, your answer would be 5.7 batches, or 5 complete batches would be a better answer.