We can rearrange the equation in order to check which option is correct:
[tex]\begin{gathered} 6x+9=12 \\ 3(2x+3)=3\cdot4 \\ 2x+3=4 \end{gathered}[/tex]The answer is option B.
NOTE: There is no direct way to find which equation is equivalent. You have to test each one or look at the coefficients and find any relationship with the original equation to see if they correspond or not.
