\[4y(y - 9) - (y - 10)(y + 3) =\]
\[= 4y^{2} - 36y - \left( y^{2} - 10y + 3y - 30 \right) =\]
\[= 4y^{2} - 36y - y^{2} + 7y + 30 =\]
\[= 3y^{2} - 29y + 30\]