Step 1: Observe the system of equations:
\[
2x + 3y = 4 \quad \text{(1)}
\]
\[
4x + 6y = 12 \quad \text{(2)}
\]
Step 2: Multiply equation (1) by 2:
\[
4x + 6y = 8 \quad \text{(3)}
\]
Step 3: Compare equation (3) with equation (2):
\[
4x + 6y = 8 \quad \text{and} \quad 4x + 6y = 12
\]
These two equations are identical, which means the lines coincide.
Thus, the correct answer is coincident straight lines.