#### Answer

$3x+y=3$

#### Work Step by Step

As the line is parallel to $3x +y =7$ they have the same slope.
We need to find the slope now:
$3x+y=7$ this means:
$y=-3x+7$
Where $-3$ is the slope.
Now, with the slope-intercept form, with m=$-3$ and passing through $(0,3)$, the equation is:
$y-y_{1}=m\times (x-x_{1})= y-3 = -3\times (x-0)$
So $3x+y=3$