What sound(s) map to the digit 7, and what's the memory hook?

7 = the "hard" /k/ and /g/ sounds (k, hard c, q, hard g).

Hook: A capital K is drawn from two 7s back to back. Examples: cow (7), cat (71), goose (hard g = 70).

Tip: Beware g — soft g ("gem") is a 6, hard g ("goose") is a 7. The sound decides, not the letter.