Multiply : \( (9x^2 + 25y^2 + 15xy + 12x – 20y + 16) \) by \( (3x – 5y + 4) \)
\[
(9x^2 + 25y^2 + 15xy + 12x – 20y + 16)(3x – 5y + 4)
\]
\[
= 27x^3 – 45x^2y + 36x^2
+ 75xy^2 – 125y^3 + 100y^2
+ 45x^2y – 75xy^2 + 60xy
\]
\[
\quad + 36x^2 – 60xy + 48x
– 60xy + 100y^2 – 80y
+ 48x – 80y + 64
\]
\[
= 27x^3 – 125y^3 – 180xy + 64
\]