Well it gets easier with experience, plus in the "real world" you'll find the restrictions are a lot more logical and easier to understand. No courier company would send 3 trucks out with 42 units of empty space just to meet some arbitrary "must be as even as possible" requirement - unless there's some REALLY good reason for it, such as the two 35's are heading due north and the 8 is heading due south.

But it might be worthwhile just running "35 35 8" past your teacher to see what he thinks of it. You may be correct that he hasn't thought it out too well. Or you may find the good reason that justifies 42 units of empty space - either way you win.