In point-slope form, the equation of the line is
.. y -k = m(x -h) . . . . . . for slope m and point (h, k)
You have m = -7/2 and (h, k) = (8, -28), so the point-slope equation is
.. y -(-28) = (-7/2)*(x -8)
.. y +28 = (-7/2)x +28 . . . . simplify
.. y = (-7/2)x . . . . . . . . . . . . subtract 28
To put this into standard form, we can multiply by 2, then add 7x.
.. 2y = -7x
.. 7x +2y = 0 . . . . . . . . . . . the standard form equation you want