Both equations are written using the slope-intercept form, that is y=mx+b. The variables. "m" and "b" represent the slope and y-intercept, respectively.
Now that you know this information, you can tell that in the first line, y=3x+4, the slope, or rise over run, is 3.
In the second line, y=3x+7, your slope is also 3. Any two lines with an identical slope will always be parallel. The only difference between these two lines, as consistent with the slope-intercept form, is your y-intercept. The y-intercept is where your line will, as the name indicates, intercept the y-axis, which is the vertical axis.
Hope this helped!