The x is your variable. The number you choose to replace x will be multiplied by four. You want the number on the left to stay smaller than the right, so it remains correct. From the given options, D is correct. 4x0 is nothing, thus making the 4 on the right bigger. Every other option multiplied by the left 4 makes it bigger, thus making the problem incorrect.
Hope this explanation helps! I'm sure you'll do great!
