i assume you mean 3x^2 + 16y = 0
so y = -3/16 x^2
The vertex is at the origin (0,0) answer
x^2 = -16/3 y
compare with standard form x^2 = 4ay:-
the focus y coordinate of the a = -16/3 / 4
= -16/12 = -4/3 so the focus is (0, -4/3) answer
and the directrix is y = 4/3 answer
