Solve please

Vlogging is an emerging trend in Pakistan as it offers a unique opportunity to earn money by posting videos on any of the websites which are freely available worldwide. Basit is a graduate from Venus University who started vlogging by posting various tutorials relating to PCB designing using many renowned software packages on his MyTube channel. The popularity of his channel is increasing with the time and he has observed that over the last few months, his channel subscribers are increasing at an average rate of 4 subscriptions per day. Keeping in view that the inter arrival time within events of desired interest is independently and exponentially distributed, determine the following: a) What is the average time between two successive user subscriptions of his channel? b) Given a user has already subscribed to his channel, what is the probability that the next person subscribes to his channel within 12 hours? c) What is the probability that there is at least an 8 hours gap between any two user subscriptions? d) What is the probability that exactly 10 users subscribe to Basit's channel in a single day