We can create two triangles for both pole and tower with their shadows. Please refer to video for the figure.
As angle made by sun at the same time are same for both tower and vertical pole.
Also, both are perpendicular to ground.
So, these two triangles are similar.
Thus,
Length of pole/Length of tower =Shadow of pole/Shadow of tower
`=>6/h = 4/28 =>h = 7**6 = 42`
So, height of tower is `42` m.