Which step he made an error and what he supposed to do instead?

Answer:
step 1
Step-by-step explanation:
[tex]for \: the \: first \: part \: of \: step \: one \: 9 {y}^{2} - 4y - 6 \: is \: correct[/tex]
however the second part of the equation is incorrectly expanded.
-(3y^2 + 6y + 2)
above states (-3y^2 add 6y add 2)
the -3y^2 is correct because a negative variable and positive variable make a negative variable
however; it should be (-3y^2 minus 6y minus 2 instead of add) because when two variables of different signs (negative and positive) are multiplied the resultant should be negative.