A sales manger receives six telephone calls on average between 9.30 a.m. and 10.30 a.m. on a weekday. Find the probability that

(a) she will receive two or more calls between 9.30 a.m. and 10.30 a.m. on Tuesday,

(b) she will receive exactly two calls between 9.30 a.m. and 9.40 a.m. on Wednesday,

(c) during a five-day working week, there will be exactly three days on which she receives no calls between 10.00 a.m. and 10.10 a.m.