Multiply each term of $ \left( \color{blue}{x-1}\right) $ by each term in $ \left( x+3\right) $.

$$ \left( \color{blue}{x-1}\right) \cdot \left( x+3\right) = x^2+3x-x-3 $$

Combine like terms:

$$ x^2+ \color{blue}{3x} \color{blue}{-x} -3 = x^2+ \color{blue}{2x} -3 $$

Multiply each term of $ \left( \color{blue}{x^2+2x-3}\right) $ by each term in $ \left( 1+x\right) $.

$$ \left( \color{blue}{x^2+2x-3}\right) \cdot \left( 1+x\right) = x^2+x^3+2x+2x^2-3-3x $$

Combine like terms:

$$ \color{blue}{x^2} +x^3+ \color{red}{2x} + \color{blue}{2x^2} -3 \color{red}{-3x} = x^3+ \color{blue}{3x^2} \color{red}{-x} -3 $$

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

$$ \left( \color{blue}{x^3+3x^2-x-3}\right) \cdot \left( 3x-9\right) = \\ = 3x^4 -\cancel{9x^3}+ \cancel{9x^3}-27x^2-3x^2+ \cancel{9x} -\cancel{9x}+27 $$

Combine like terms:

$$ 3x^4 \, \color{blue}{ -\cancel{9x^3}} \,+ \, \color{blue}{ \cancel{9x^3}} \, \color{green}{-27x^2} \color{green}{-3x^2} + \, \color{orange}{ \cancel{9x}} \, \, \color{orange}{ -\cancel{9x}} \,+27 = 3x^4 \color{green}{-30x^2} +27 $$