$$ (qrstx-3)^4 = (qrstx-3)^2 \cdot (qrstx-3)^2 $$

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

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

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

$$ \begin{aligned}\left(qrstx-3\right)^2 = \color{blue}{\left( qrstx \right)^2} -2 \cdot qrstx \cdot 3 + \color{red}{3^2} = q^2r^2s^2t^2x^2-6qrstx+9\end{aligned} $$

Multiply each term of $ \left( \color{blue}{q^2r^2s^2t^2x^2-6qrstx+9}\right) $ by each term in $ \left( q^2r^2s^2t^2x^2-6qrstx+9\right) $.

$$ \left( \color{blue}{q^2r^2s^2t^2x^2-6qrstx+9}\right) \cdot \left( q^2r^2s^2t^2x^2-6qrstx+9\right) = \\ = q^4r^4s^4t^4x^4-6q^3r^3s^3t^3x^3+9q^2r^2s^2t^2x^2-6q^3r^3s^3t^3x^3+36q^2r^2s^2t^2x^2-54qrstx+9q^2r^2s^2t^2x^2-54qrstx+81 $$

Combine like terms:

$$ q^4r^4s^4t^4x^4 \color{blue}{-6q^3r^3s^3t^3x^3} + \color{red}{9q^2r^2s^2t^2x^2} \color{blue}{-6q^3r^3s^3t^3x^3} + \color{green}{36q^2r^2s^2t^2x^2} \color{orange}{-54qrstx} + \color{green}{9q^2r^2s^2t^2x^2} \color{orange}{-54qrstx} +81 = \\ = q^4r^4s^4t^4x^4 \color{blue}{-12q^3r^3s^3t^3x^3} + \color{green}{54q^2r^2s^2t^2x^2} \color{orange}{-108qrstx} +81 $$

Combine like terms:

$$ q^4r^4s^4t^4x^4-12q^3r^3s^3t^3x^3+54q^2r^2s^2t^2x^2-108qrstx+ \color{blue}{81} + \color{blue}{3} = \\ = q^4r^4s^4t^4x^4-12q^3r^3s^3t^3x^3+54q^2r^2s^2t^2x^2-108qrstx+ \color{blue}{84} $$