Complete the Puzzle: Identify the Missing Composite Number

To solve this problem, we will find a composite number in the form of a two-digit number with 3 as the unit digit.

First, let's define what a composite number is: a number with at least one divisor other than 1 and itself.

We'll now check all the possible numbers $\square 3$ given the choices:

• Number 1: $03$, not valid as it is less than 10.
• Number 2: $13$, only divisors are 1 and 13, hence prime not composite.
• Number 3: $23$, only divisors are 1 and 23, hence prime not composite.
• Number 4: $33$, divisors are 1, 3, 11, and 33, hence it is composite.

From the choices, the correct answer is $\boxed{9}$.

The number we filled in is thus $93$, which indeed is a composite number.

Thus, the solution to the problem is to fill the blank as $9$, making the number $93$.