Start by numbering the longest chain:

There are 8 carbons in the longest chain: oct-

There are only single bonds: -ane

This eliminates option 4.

There are two ethyl groups: diethyl

There is 1 isopropyl group: isopropyl

There are 4 methyl groups: tetramethyl

If we start counting from the left most carbon, our first alkyl group will be on the 2nd carbon. If we start counting from the right most carbon, our first alkyl group will be on the 3rd carbon. Therefore we should start counting from the left, and therefore our isopropyl group will be on the 5th carbon, so we can eliminate option 2. 

Lastly, we want to name the molecule in alphabetical order (ethyl, isopropyl then methyl), so we can eliminate option 1.

Making option 3 the correct answer. 

For more information, visit our organic chemistry page!