Question 70753
In the general equation of the line y=mx+b the constant b is the y intercept. So all you need to do is solve for y and find the value which will satisfy this equation. 

{{{cross(3x-3x)+y=7-3x}}} Subtract 3x from both sides 
{{{y=7-3x}}}
{{{y=-3x+7}}}could be written as this as well
In this case b=7 so the y-intercept is (0,7)