customers arrival process $\{$Nt$\}$t in $[0,\backslash$infty $)$ at the Sin Kee$$s Chicken Rice store

is governed by the Poisson process with rate $4.$

$($a$)(3$ pts$)$ Write down the random variable that represents the time of arrival of the $3$rd customer

in terms of T$1,...,$ T$3.$ What is the expected time of arrival of the $3$rd customer?

$($b$)(3$ pts$)$ What is the expected time le