Find $ \left(10x-9\right)^2 $ using formula.

$$ (A - B)^2 = \color{blue}{A^2} - 2 \cdot A \cdot B + \color{red}{B^2} $$

where $ A = \color{blue}{ 10x } $ and $ B = \color{red}{ 9 }$.

$$ \begin{aligned}\left(10x-9\right)^2 = \color{blue}{\left( 10x \right)^2} -2 \cdot 10x \cdot 9 + \color{red}{9^2} = 100x^2-180x+81\end{aligned} $$

Find $ \left(3x-7\right)^2 $ using formula.

$$ (A - B)^2 = \color{blue}{A^2} - 2 \cdot A \cdot B + \color{red}{B^2} $$

where $ A = \color{blue}{ 3x } $ and $ B = \color{red}{ 7 }$.

$$ \begin{aligned}\left(3x-7\right)^2 = \color{blue}{\left( 3x \right)^2} -2 \cdot 3x \cdot 7 + \color{red}{7^2} = 9x^2-42x+49\end{aligned} $$

Remove the parentheses by changing the sign of each term within them.

$$ - \left( 100x^2-180x+81 \right) = -100x^2+180x-81 $$

Multiply each term of $ \left( \color{blue}{8x^3-100x^2+180x-81}\right) $ by each term in $ \left( 9x^2-42x+49\right) $.

$$ \left( \color{blue}{8x^3-100x^2+180x-81}\right) \cdot \left( 9x^2-42x+49\right) = \\ = 72x^5-336x^4+392x^3-900x^4+4200x^3-4900x^2+1620x^3-7560x^2+8820x-729x^2+3402x-3969 $$

Combine like terms:

$$ 72x^5 \color{blue}{-336x^4} + \color{red}{392x^3} \color{blue}{-900x^4} + \color{green}{4200x^3} \color{orange}{-4900x^2} + \color{green}{1620x^3} \color{blue}{-7560x^2} + \color{red}{8820x} \color{blue}{-729x^2} + \color{red}{3402x} -3969 = \\ = 72x^5 \color{blue}{-1236x^4} + \color{green}{6212x^3} \color{blue}{-13189x^2} + \color{red}{12222x} -3969 $$