2. From the moment, we can know that when the left and right moments are equal, they will be balanced, that is, the moment on the left should be 3x 10=30, so the left should put 10 on the scale of 3, 6 on the scale of 5, or 30 on the scale of 1.

3. Balance time: the number of left pieces x the left scale = the number of right pieces x the right scale, which can solve the first two problems.