\begin{array}{l}
{x^4} - 16{x^3} + 95{x^2} - 248x + 240 = 0\\
{x^4} - 3{x^3} - 13{x^3} + 39{x^2} + 56{x^2} - 168x - 80x + 240 = 0\\
{x^3}\left( {x - 3} \right) - 13{x^2}\left( {x - 3} \right) + 56x\left( {x - 3} \right) - 80\left( {x - 3} \right) = 0\\
\left( {x - 3} \right)\left( {{x^3} - 13{x^2} + 56x - 80} \right) = 0\\
\left( {x - 3} \right)\left( {{x^3} - 5{x^2} - 8{x^2} + 40x + 16x - 80} \right) = 0\\
\left( {x - 3} \right)\left( {{x^2}\left( {x - 5} \right) - 8x\left( {x - 5} \right) + 16\left( {x - 5} \right)} \right) = 0\\
\left( {x - 3} \right)\left( {x - 5} \right)\left( {{x^2} - 8x + 16} \right) = 0\\
\left( {x - 3} \right)\left( {x - 5} \right){\left( {x - 4} \right)^2} = 0
\end{array}