A stone is thrown vertically upward with an initial velocity u from the top of a tower, reaches the ground with a velocity 3u. The height of the tower

• A.  \[\frac{3{{u}^{2}}}{g}\]                
• B.         \[\frac{4{{u}^{2}}}{g}\]  
• C.  \[\frac{6{{u}^{2}}}{g}\]                
• D.         \[\frac{9{{u}^{2}}}{g}\]