Question 988271
Hi there,
Consider the mast and wires as a right
angled triangle.
The wire is the hypotenuse
The mast is the opposite side
The mast size^2 + ground length^2 
= wire length^2
So, 40^2 + 20^2 = wire length^2
1600 + 400 = wire length^2
wire length^2 = 2000
wire length = √2000
wire length = 44.721
3 wires = 3 x 44.721
3 wires = 134.2ft
Hope this helps :-)