The length of time $($in seconds$)$ an individual takes to use an ATM is Normally distributed with mean $100$ and standard deviation $10.$

When Jackson arrives at an ATM, he finds $4$ individuals waiting in a queue to use the machine. Let T be the duration $($again$,$ in seconds$)$ of the period that starts when the first individual in queue accesses the ATM and ends when the last individual in queue leaves the ATM.