Answer
Last step is wrong.
Work Step by Step
The given equation is
$\Rightarrow 6(2y+6)=4(9+3y)$
Use distributive property.
$\Rightarrow 12y+36=36+12y$
Subtract $36$ from each side.
$\Rightarrow 12y+36-36=36+12y-36$
Simplify.
$\Rightarrow 12y=12y$
Subtract $12y$ from each side.
$\Rightarrow 12y-12y=12y-12y$
Simplify.
$\Rightarrow 0=0$
The statement $0=0$ is always true. So, the equation is an identity and has infinitely many solutions.
Hence, the last step is wrong.
