An emergency flare is fired from a vehicle. Its height, h metres is given by h(t)=-5t^2+35t+50, where t is the time in seconds. A)What is the maximum height reached by the flare? B and C of question

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The maximum height is given by the h coordinate of the vertex of the parabola.  To find this you need to find the t coordinate.You can find the t coordinate (or the time to reach max h, part B) by using the formula -b/2a, where b is the t coefficient (or 35 in this case) and a is the t^2 coefficient (or -5).  So the time to reach the maximum height (units along the t-axis) is:-35/(2*-5), or 7/2 time units.  Then find the maximum height by plugging this t-value into the equation and solving for h(7/2).To find how long it takes to hit the ground, solve for when t=0.  This equation isn't easily factored, so use the quadratic formula.  You'll want the largest t value, of the two, or the nonnegative value.