You have to take the longest chain with the functional group as the main chain. Which means the name will end in ‘hex-1-ene’. The ‘1’ is for the place of the functional group. This has to be the smallest number possible. So no ‘hex-5-ene’. Then for the first part, we need to say something about the place and the kind of the branch. In this case, it is a propylgroup on the 4th carbon of the main chain. We will not take the 3rd carbon because we already decided to count from the right. The total name will then be: ‘4-propylhex-1-ene’.