This scenario was depicted in one of Rembrandt's lost works,
The Three Guide Wires. Here's a photograph of the painting:
Not to scale.
The brown box represents the pole and the blue line represents one of the wires. The eyelet (yes, there's supposed to be an eyelet in there) is on the ground [MATH]20[/MATH] feet away from the pole, and the wire attaches to it and the pole [MATH]30[/MATH] feet up. The tied end of the wire where it meets the eyelet makes up an additional [MATH]1\frac{1}{3}[/MATH] feet.
There are three such wires. The problem asks for the total measurement of how much wire is needed, rounded to the next multiple of 5.
A triangle is formed between the pole, the ground and the wire. Where the pole meets the ground, a [MATH]90^{\circ}[/MATH] angle is formed. Therefore, the length of wire between the pole and the ground forms this triangle's hypotenuse.
To solve for the problem, calculate the length of this hypotenuse (the primary length of the wire), add [MATH]1\frac{1}{3}[/MATH] (the allowance for fastening the wire), multiply the result by [MATH]3[/MATH] (the number of wires), then round up to the next multiple of 5 if needed.