One, two, and three motor steps separate per-step work from total useful output. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
One checked step uses twelve joules
Force 6 newtons over step 2 metres gives per-step work 12 joules.
6⋅2=12
Two steps double the useful output
The per-step work stays 12 joules. With 2 steps, useful work is 24 joules.
2⋅12=24
Three steps make the audit's useful work
Three steps at 12 joules per step total 36 joules, the useful-work source used by the audit.