Answer
$y=-4x+28$
Work Step by Step
A linear function has the form $y=mx+b$, where $m$ is the slope, $b$ is the y-intercept.
A linear function can also have the form $y-y_1=m(x-x_1)$, where $m$ is the slope, and $(x_1,y_1)$ is a point on the line.
Hence here because the x-intercept is $(7,0)$, the line contains this point: $y-0=-4(x-7)\\y=-4x+28$