Please help! i am not doing too good in math and i need help with a few of my questions

The height of a flare fired from the deck of a ship in distress can be modeled by h(t)= -2(8t^2-52t-28), where h is the height of the flare above water and t is the time in seconds. a. find the time it takes the flare to hit the water.

Can you me find the missing length. i attached an image.

Pls the last one and it has to be like number 6