I hope your question is to find whether y(y+4)-y squared =6 is a quadratic equation or not.
Let's simplify the left side of the equation. So,
y (y + 4) - y²
= y² + 4y - y²
= 4y Since y² and -y² has cancel out.
So, the above equation changes to
4y = 6.
Notice here the square term has vanish.
So, it's not a quadratic equation.
I hope it's helps you!