Step 1: Align TODAY with 45733: T=4, O=5, D=7, A=3, Y=3.
Step 2: Align WROTE with 10542: W=1, R=0, O=5, T=4, E=2 — O repeats as 5, confirming the match.
Step 3: Check DATE-7342 and DIRTH-79046 for consistency: D=7, A=3, T=4, E=2, R=0 all agree with the earlier mapping.
Step 4: Since O consistently equals 5 in two independent words, the digit 5 represents O.
\[ \boxed{O} \]