Determine the T Intervals on Which the Curve $x = 6 t ^ { 2 } , y = t ^ { 3 } - 3 t \text { is concave }$

Multiple Choice

Determine the t intervals on which the curve $x = 6 t ^ { 2 } , y = t ^ { 3 } - 3 t \text { is concave }$ downward or concave upward.

A) concave downward: $- \infty < t < 0$ ; concave upward: $0 < t < \infty$
B) concave downward: $0 < t < \infty$ ; concave upward: $- \infty < t < 0$
C) concave downward: $- 6 < t < 3$ ; concave upward: $0 < t < 3$
D) concave downward: $- 6 < t < 0 ;$ concave upward: $0 < t < \infty$
E) concave downward: $- \infty < t < 0$ ; concave upward: $0 < t < 3$