A 30 meter deep well, with a diameter of 7 meters is dug and the earth from digging is evenly spread out to form a platform of size 22 meters by 14 meters. The height of the platform is:

The well is dug which will resemble a shape of cylinder with a diameter of 7 m and height equal to 30 m.
Hence, the volume of earth which is obtained by digging well will be = $$\pi\ \left(r\right)^2\left(h\right)$$
                              Volume = $$\dfrac{\ 22}{7}\left(3.5\right)^2\left(30\right)\ $$

As we are using the entire earth to make a platform of certain height, it will resemble a cuboid whose volume should be ''(L)(B)(H)".
                                           Given : L = 22 m, B = 14 m .
So, $$\dfrac{\ 22}{7}\left(3.5\right)^2\left(30\right)\ $$ = (22)(14)(H)

Therefore, H = 3.75 metres