You can figure this out if you just count the longest chain of carbon. The longest is 4 chains so so you know that the figure is a butane.
It is not a butene because here are no double bounds, you know it is not a butyne because there are no triple bonds. That means that 3rd and 4th choice is not the answer.
Then next you indicate the placement of the branch. There is only one branch on methyl, so you can rule out the 1st and last choice.
You are then left with 2-methylbutane.
