If increasing 15 by n% is equivalent to decreasing 75 by n%, then what is 6% of n?

15(1 + n/100) = 75(1 - n/100)
15 + 0.15n = 75 - 0.75n
0.15n + 0.75n = 75 - 15
0.9n = 60
n = 60/0.9 = 66 2/3%

6% of n = 0.06 x 66 2/3 = 4