slope-intercept form of a line (L1): y = mx + b; where m is the slope and b the y - intercept.
If two lines are parallel, that means the slope of both equations are equal.
L2: y = 3x - 7, m = 3
So, m for L1 is m = 3.
Now we just need to find y - intercept, as follows:
L1 passes through (0,4), then:
4 = 3(0) + b
4 = 0 + b
b = 4
The equation for the line is y = 3x + 4