The balance on the left shows the problem  2x + 4 = 10. We are looking for x, or the number of blocks in one bag.

Take away 4 blocks from each side. The scale will stay balanced because both sides are losing the same amount of weight.

That leaves 2 bags on the left, 6 blocks on the right. If each bag has the same amount, then each has to have 3 blocks. And that’s it!

Each bag has 3 blocks, so x = 3.