The equation of the line passing through point $ \left(0,~9\right) $, and point $ \left(3,~1944\right) $ is:
$$ 645x-y+9=0 $$To find equation of the line passing through points $ A(x_A,y_A) $ and $ B(x_B,y_B) $, we use formula:
$$ y - y_A~=~\frac{y_B - y_A}{x_B - x_A}(x-x_A) $$In this example we have:
$$ \begin{aligned} & \left(0,~9\right) \implies x_A = 0 ~~\text{and}~~ y_A = 9 \\[1 em] & \left(3,~1944\right) \implies x_B = 3 ~~\text{and}~~ y_B = 1944 \end{aligned} $$After substituting into the formula, we obtain:
$$ \begin{aligned} y - y_A~&=~\frac{y_B - y_A}{x_B - x_A}(x - x_A) \\[1 em] y - 9~&=~\frac{ 1944 - 9 }{ 3 - 0 } \left( x - 0 \right) \\[1 em]y - 9 ~&=~ 645 \left( x - 0 \right) \\[1 em]y - 9 ~&=~ 645x + 0 \\[1 em]y ~&=~ 645x + 9 \end{aligned} $$