In the lesson they had like these little scales, with boxes on both sides? Frankly it didn't make sense to me either.

Lovely common core we are dealing with the same thing. If ds doesn't use their model he gets the answer wrong even if he actually got it right

Well, using the Singapore method, the bar model would look like a long narrow horizontal rectangle, which you divide into halves with a small vertical line in the middle. Then you label the complete long bar "6", indicating that it is 6 units long, and each of the small sub-bars "3", indicating that they are 3 units long.

My feeble attempt at a bar model:

.________6________
[________]________]
. . . .3 . . . . . 3

Do let us know what the teacher says.

I've been waiting to get this back to you, but the grades just finally came in. So, she got the problem wrong, but the teacher added this comment:

"Hi DD, I appreciate that you prefer to think of the problem in equation form. However, part of learning is trying to understand things in another way. Curriculum asks students to do this frequently in the course. Please do the best you can to try, even struggle, with the models and questions that you are given.

Great job with your equation representation. You did an excellent job of explaining your thinking!"

To be honest, this is some thoughtful and kind feedback. I still think the model thing is silly, but I can't argue with "you're being asked to think this way, so TRY."

Edited to add: she actually got 4 of 6 points on that question.