DNA mutations in CHO-KI mammalian cells
I suspect this question is a lot easier than it makes itself out to be, though I may not be thinking straight. It doesn't matter how many cells you start with or how many doublings there are. Nor, for that matter, does it matter how many genes each cell has. There's a 2% chance that a random mutation will affect "crucial genetic information"; I must assume that that refers to genes. So $0.02*4000=80$ mutations would be expected to affect genes.