You have to give the substituents the smallest number possible.
First you have to identify the longest chain. And then you start numbering the carbons of that chain.
You have 1 methyl group on C3, on C4 you have a (1-methylpropyl) group and on C5 you have an isopropyl group.
That weird group on C4, since it's has a branch, which is a methyl group, you have to give its position in relation to the propyl group. That position is 1.
I think IUPAC accepts the isopropyl name; propyl because there's 3 carbons and iso because the group is symmetrical.
The final name has to be in alphabetical order.