This seems more like a prob or stats question than calculus but whatever. Let's call A the mass distribution of grade A papayas and B the mass distribution of grade B papayas. Well then,

and

a) We want 3 grade A papayas so the distribution is . So, . To find the probability, use a normal distribution table to find:

b) Same logic,

c) Let X= A+A+...+A (six times) -B-B-...-B (seven times)

then,

So to have 6 A papayas heavier than 7 B papayas means that X>0.