Hi!
Switch up the variables:
y = -14x - 2.
x = -14y - 2.
Add 2 to both sides.
x + 2 = -14y - 2 + 2.
x + 2 = -14y.
Divide by -14 on both sides.
(x + 2) / -14 = -14y / -14.
(x + 2) / -14 = y.
Change the y to f^-1(x).
f^-1(x) = (x + 2) / -14.
Hopefully, this helps! =)