(A): `-h=ut_(1)-1/2g t_(1)^(2) …(i)`

(B) `h=ut_(2)+1/2g t_(2)^(2) …(ii)`

From (i), `u=-h/t_(1)+1/2g t_(1)`

From (ii), `u=h/t_(2)-1/2 g t_(2)`

`-h/t_(1)+1/2 g t_(1)=h/t_(2)-1/2 g t_(2)`

`(h(t_(1)+t_(2)))/(t_(1)t_(2))=1/2g (t_(1)+t_(2))`

`h=1/2g t_(1)t_(2)`

(c ): `h=1/2 g t^(2)`

`1/2g t_(1)t_(2)=1/2g t_(2)`

`t=sqrt(T_(1)t_(2))`