Solve for the Yellow Box: Finding the Missing Number in 68 - □ = 12

To solve this problem, let's follow the steps below:

• Step 1: Identify the value of the yellow shape.
  According to the problem, the value of the yellow shape is $12$.
• Step 2: Substitute this value into the subtraction expression.
  The expression becomes $68 - 12$.
• Step 3: Perform the subtraction operation.
  Calculate $68 - 12$ as follows:

$68 - 12 = 56$

The steps for subtraction are:
Break down $68 - 12$ into simpler components:
Subtract the units: $8 - 2 = 6$
Subtract the tens: $6 - 1 = 5$
Combine the results: $56$

Therefore, the solution to the problem is $56$.

The correct choice from the provided options is $\boxed{56}$.