We use the formula,
[tex]h= ut- 16 t^2[/tex]
Here, h is the variable represents the height of the flare in feet when it returns to the sea so, h = 0 and u is the initial velocity of the flare, in feet per second and its value of 192 ft/sec.
Substituting these values in above equation, we get
[tex]0 = 192 t - 16 t^2 \\\\ 16 t( 12 - t ) =0 \\\\ t = 12 s[/tex].
Here, t= 0 neglect because it is the time when the flare is launched.
Thus, flare return to the sea in 12 s.