This is the boss. No calculator — today $g = 10\ \mathrm{N/kg}$, the round number every engineer keeps for mental work and site sanity checks, and the values are chosen to fit in your head. One gantry, one long problem, and every answer feeds the next: weight, then the moment about the far leg, then the reaction that balances it, then the friction that reaction buys, then the verdict. Write each line down as you go — one early slip rolls all the way to the floor.

And note what the last line actually asks. It does not want another number; it wants a DECISION, the way a real check does. The arithmetic is only there to earn you the right to make it.

Everything in the chapter rides in this one rig. 5★ under par here is the chapter crown. Clock in.