I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.
So your j loop, which I assume you want to loop over the INNER arrays, should probably not be comparing to cars.length. Instead, at the first iteration (when i==0), you want to be setting j to cars.length-1. At the next iteration, when i==1, you want j to equal cars.length-1.
Each sub-array is found at a given index in the cars array. Can you think of a way, inside that inner loop, to get that? Hint: think about i.