There are two solutions.
.. (3, 2)
.. (0.2, -3.6)
_____
If you're choosing possibilities from a list, trying them in the equations usually gives quick results.
For the fourth term r = 3
Fourth term = 6C3(x)^(6 - 3) (4y)^3 = 20x^3 (64y^3) = 1,280x^3y^3
That would be 156%. have a great day