Using the diameter, we can find the circumference of the wheel.
Circumference = 2 * pi * radius
To find the radius, divide the diameter by 2. 6/2 = 3; your radius is 3.
2 * pi * 3 = 6 pi.
The circumference is 6pi. Leave it like this for an accurate answer in the next step.
If the rope can wrap around the wheel 3 times, then it can do 3 times the circumference.
3 * 6pi = 18pi
18pi ≈ 56.549 meters (round to whatever decimal you deem fit for 18pi).
The length of the rope is 18pi or approximately 56.549 meters long.
Realistically though, the answer would be more than 18pi meters long because the problem does not say it wraps around exactly 3 times. It just says it can completely wrap around the wheel. That's not what you should go with though; that's just me being nit-picky.