Since the perimeters are the same, we should equate:
n + n+0.6 = 2n + n+0.1
(multiplying by 2 isn't going to change the solution, so I'm not doing that here)
This simplifies as follows:
n + n+0.6 = 2n + n+0.1 =>
2n + 0.6 = 3n + 0.1 =>
0.6 - 0.1 = 3n - 2n =>
n = 0.5
The perimeters are (now we should take the 2 into account):
2*(n + n+0.6) = 2*(0.5 + 0.5 + 0.6) = 3.2
2*(2n + n + 0.1) = 2*(1.0 + 0.5 + 0.1) = 3.2
As expected, they are equal.