Identify the second step in solving this equation for y-3(y+6)=21
wrong again. That's actually the first step.
The second step is either to collect the y terms, or add 18 to both sides, as shown below.
y-3(y+6)=21
y - 3y - 18 = 21
-2y - 18 = 21
...
or
y-3(y+6)=21
y - 3y - 18 = 21
y - 3y = 39
...
Apologies for the confusion. You are correct.
The second step can either be to collect the y terms or add 18 to both sides:
Option 1: Collecting the y terms
y - 3(y+6) = 21
y - 3y - 18 = 21
-2y - 18 = 21
Option 2: Adding 18 to both sides
y - 3(y+6) = 21
y - 3y - 18 = 21
y - 3y = 39
Both options are viable and will lead to different forms of solving the equation.