Hi, i'm very new to this forum and i am stuck on this problem. Perhaps i'm just having a brain freeze, but i'd like to know how to solve this question.Thanks . And apologies if this is in the wrong part of the forum.

The height, h(t) metres, of a batted baseball as a function of the time, t seconds, since the ball was hit can be modelled by the function:

$\displaystyle h(t)=-2.1(t-2.4)^2 +13$

Question: How many seconds after it was hit did the ball hit the groud, to the nearest tenth of a second?

The answer key tells me 4.9 seconds, however, i am unable to arrive at that answer. My idea was to substitute h(t) with 0 to get the x intercept, but the numbers greatly confused me.

Any help? Thanks in advance