Select the description that is true of the equation 3x + y = 7. x-intercept equals -7 x-intercept equals 7 y-intercept equals 7 < is it this? y-intercept equals -7

I believe it is that one

To find the y-intercept the equation can be written in slope-intercept form
y=mx+b where m is the slope and b being the y-intercept
solving 3x+y=7 for y will give you
y=-3x+7 
The answer is the third option
y-intercept equals 7

hope this helped