Which substitution turns y′+y=y4exy' + y = y^4 e^xy′+y=y4ex into a linear equation?
v=y−3v = y^{-3}v=y−3
v=y3v = y^3v=y3
v=y−4v = y^{-4}v=y−4
v=y4v = y^4v=y4