well, first off let's take a peek of what is the slope of "y" in this case hmmm

so, is 1/2 ok....
now, a line that is perpendicular to that equation, will have a slope that is
negative reciprocal of that.

so, what is the equation of a line whose slope is -2 and passes through (0,6)?
![\bf \begin{array}{lllll} &x_1&y_1\\ % (a,b) &({{ 0}}\quad ,&{{ 6}})\quad \end{array} \\\\\\ % slope = m slope = {{ m}}= \cfrac{rise}{run} \implies -2 \\\\\\ % point-slope intercept y-{{ y_1}}={{ m}}(x-{{ x_1}})\implies y-6=-2(x-0)\\ \left. \qquad \right. \uparrow\\ \textit{point-slope form} \\\\\\ y-6=-2x\implies y=-2x+6]()