When my students were working with solving first level equations, I started to make these problems to help them see a more concrete model next to the symbolic algebra. Eventually, it became this: A unit that moves students from the concrete to the abstract in careful steps. You get:
Part 1: Basic equations to variables on both sides
Part 2: The Distributive Property
Part 3: Substitution property for systems
I tended to avoid dealing with negative numbers where I could, as that comes in at