equation of line is y=mx +c , where c is the y-intercept. And the line parallel to y=mx+c, will be
y=mx + k, where k is any integer.
so, in your case you need the equation of the parallel line will be y=3x + k.
So k is your x-intercept.
Example:
Let the line parallel to y =3x+3/4 pass through the point (0,1) then its intercept would be.
1=0x+k
k=1.