
Plant no more roses, i.e. option a
MRS of given utility function is 802r
So, user for interior solution will try to maximize his utility by
MRS = P1/P2 ..........(1)
P1/P2 = 4
while P1/P2 is constant, hence the MRS.
Thus r will be a constant ,i.e 42 roses when you solve eq 1 such that utility can be maximized.
Thus upon adding more land, he will not change his consumption of roses.
While, on a close look, u will see its a quasilinear preference
i.e.
U(z,r) = z+80rr^2 = k
Z= k  v(r)
hence no change in consumption of r upon addition of more income(land here).
