B.3. There are many ways to go about getting this answer. The most confortable way for me, and it may not be the fastest, is to find what each machines individual rate is.
rate=(x+x+x+x+x+x), where x=the rate of each individual machine.
Therefore, 1=(x+x+x+x+x+x)(12), deduce x=1/72.
Now that you have that, use:
1(job)=rate*8(days). You know that the rate=(x+x+x+x+x+x+ax), where a is the number of extra machines. Try values in the answer to see what works. I got 3, B. I would like to know how other s got this answer, I know there is a faster way, even though this took me about 1.5 minutes.