Which? There are no choices.
d = -16t²+ 1000
We want a height greater than 300, that's
d > 300
Answer: -16t²+ 1000 > 300
Since we don't have the list I'll continue to solve, generating equivalent inequalities along the way.
-16t²+ 1000 > 300
-16t² > -700
16t² < 700
t² < 700/16
Assuming t ≥ 0,
t < (5/2)√7