$[20$ pts$.]$ Suppose seven stations are waiting for another packet to finish on an

Ethernet. All transmit at once when the packet is finished and collide. Answer the

following questions:

a$.[10$ pts$]$ What is the probability all of them transmit at once and collide again

on their second attempt to transmit?

b$.[10$ pts$]$ What is the smallest number of collisions that are bound to happen

before each of the seven stations successfully delivers one packet? $[$P$.$S$.$ If

multiple stations transmit at once and collide, then we count this as one

collision.$]$