Suppose 4x 2 + 9y 2 = 36, where x and y are functions of t

Suppose 4x 2 + 9y 2 = 36, where x and y are functions of t.

(a) If dy/ dt = 1/3, find dx / dt when x = 2 and y = 2/3 √5.
(b) If dy/ dt = 3, find dx / dt when x = 2 and y = 2/3 √5.