Please help me! And explain how you got your answer

Aman steps out of a plane at a height of 4,000m above the ground falls 2,000m very quickly and then opens his parachute and slowly falls the remaining 2000m to the ground what height above the ground would be the best choice for a reference point

Enter the number of complex zeros for the polynomial function in the box. f(x) = x+ + 5x² +6

This is so hard and it’s for a test