A basketball player, standing near the basket to grab a rebound, jumps 73.6 cm vertically. How much time does the player spend in the bottom 15.4 cm of the jump?

I need someone to check my work.

I got about 3.797 as the inital velocity. I plugged this into "x = vt + 1/2at^2" and used the quadratic formula to get 0.81391 for t.

Now...do I have to times this number by 2 to get the answer? If not, what exactly do I do?