Step 1: First we have to write polynomials in descending order.
$$ \begin{aligned} P(x) &= 2x^4+x \\ Q(x) &= -2x^2+7x \\ \end{aligned} $$Step 2: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrrr} & 2x^4 & & x \\ \color{blue}{ + } & & -2x^2 & 7x \\ \hline \end{array} $$Step 3: Combine like terms (add each column):
$$ \begin{array}{lrrr} & 2x^4 & & x \\ \color{blue}{ + } & & -2x^2 & 7x \\ \hline & 2x^4 & -2x^2 & 8x \end{array} $$