Let x and y be the second and third wire.
Solve for the length of the second wire
x= 5.6 m + 4.2 m <-- add 4.2 to 5.6 since the second wire is longer which means the length should increase.
x = 9.8 m <-- length of the 2nd wire
Solve for the length of the third wire
y= x - 4.9 m
y = 9.8 m - 4.9 m <-- subtract 4.9 from 9.8 since the third wire is shorter
y= 4.9 m <-- length of the third wire
So the length of the third wire is the closest to 5 m.