Checkpoint: frames all the way down

f(5) opened four frames before any addition happened: 5, 3, 1, then the base case f(-1) = 1. Unwinding gives 5 + 3 + 1 + 1 = 10 — check that arithmetic against your own table; the tests are the referee. If your table disagreed with your first guess, that disagreement is exactly the skill being built: trust the frame-by-frame trace, not the impression.