4/ A civil engineering firm is interested in modeling the time taken to complete a specific phase of road construction, such as laying a certain type of pavement, which requires a series of sequential tasks. let's assume that the time taken to complete each sub-task follows an exponential distribution. The average time taken for each sub-task is 2 days. The phase involves a sequence of 5 such sub-tasks that need to be completed one after the other. What distribution is used and determining parameters?