Higher Order Derivatives

An object is thrown straight up in the air at t=0t = 0 seconds. Its height in metres at tt seconds is given by

h(t)=s0+v0t7t2h(t) = s_0 + v_0 t - 7t^2
where s0s_0 and v0v_0 are constants. In the first second the object rises 7 metres. For how many seconds does the object rise before starting to fall back down?
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