s = floor(n/11)
h = n % 11 (where % is the remainder of n / 11)
Point out to him/her that, since he/she has now subtracted everything he/she began with, he/she can hardly be giving away any secret by telling you his/her final answer.
Neverhteless, when he/she tells you his/her answer, you proceed to name both the suit and the value of the two cards he/she has chosen.
Can you work out how that detailed information can be derived from the simple answer he/she has given you?