Let AB be a guy wire attached to a pole BC of height 18 m. Now, to keep the wire taut let it to be fixed at A.
Now, In right triangle ABC
By using Pythagoras theorem, we have
AB2 = BC2 + CA2
⇒ 242 = 182 + CA2
⇒ CA2 = 576 − 324
⇒ CA2 = 252
⇒ CA = 6√7 m
Hence, the stake should be driven 6 √7m far from the base of the pole.