Solve the Addition Equation: Finding the Missing Number in □ + 30 = 42

To solve this problem, we'll follow these steps:

• Step 1: Recognize that the yellow shape represents the number 12.
• Step 2: Replace the shape in the equation with its numeric value.
• Step 3: Perform the addition.

Now, let's work through these steps:
Step 1: The problem states that the yellow shape is equivalent to $12$.
Step 2: We replace the yellow shape with $12$ in the addition equation.
Step 3: Solve the equation $12 + 30 = 42$. This addition gives us the solution.

Therefore, the solution to the problem is $42$.