Linda From Maine wrote:
Also, the photo you uploaded is not a 4x6 aspect. Be sure to do your crop first. Then when you export and do the re-size option, when you change the width to 3000, it will automatically do the other number as 2000.
Here is what a 4x6 would look like. #2 is what you posted.
Rather than crop for an aspect ratio I crop for the subject, but then you’ll need to do a little math and figure out which edge to base your resize on so that the other edge is less than the max allowed. Lightroom lets you specify either a long or short edge to set the value to and it automatically sets the other to maintain the aspect.