Clearly X = {100, 200, 300, 400, 500, 600, 700, 800, 900}And for the equation x3+3ax2 + (298a + 299) x - 2 = 0 to have positive point of maxima.The equation f'(x) = 0 should have both the roots positive and unequal, which gives a > 299 . ∴ Y = {a ; a > 299} ∴ Number of elements in X ∩ Y = 7