The problem statement, all variables and given/known data

Question

A body is thrown upward and remains in air for 10 seconds , the initial velocity at which it was thrown in is?

The attempt at a solution
g = -10 , t = 10 s , vf = 0 , vi = ?

Vf = vi + gt
0=vi + (-10) (10)
Vi = 100

but its answer is not 100 its answer is 50 help me please , where I did a mistake ? Thanks

Answer 1

vf=-vi as it returns to ground.

-vi=vi+at
2vi=100
vi=50