see it is a linear motion & not a motion of a parabola because no  angle is mentioned.

 

when the body goes up it is at a heigth 80m from the ground and while coming down also it is 80m from the ground. now lets know what is height at two times now consider that the body is moving up let it be at 80m from the ground now from there till it comes back to the same point the time taken is 6s {i.e.the ball going up till its maxium heigth & again coming back to the same point (80m from the ground)}  

 

did u get me

 

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