Question 1004544
For each Tree we need equal number of three wires from Tree trunk to the ground.

A simple Trigonometry will solve the question, thus;

Using Pythagoras, (Sum of the squares of the Adjacent and Opposite equals the square of the Hypotenuse)
{{{Hyp^2 = Adj^2 + Opp^2}}}

{{{Hyp^2 = 4^2 + 3^2}}}
{{{Hyp^2 = 16 + 9 }}}

{{{Hyp = sqrt(25)}}}
{{{Hyp = 5 }}}

So for one rope, you will need 5Ft. Therefore you will be needing 5 X 3 for each Tree. => 15.
  The entire pack of six Trees will be 15x6 => 90.

Final Answer = 90 Ft.