[tex]\frac { n }{ 100 } \cdot 4,000=600\\ \\ 4,000\cdot n=60,000\\ \\ Therefore:\\ \\ n=\frac { 60,000 }{ 4,000 }[/tex]
[tex]\\ \\ =\frac { 60\cdot 1,000 }{ 4\cdot 1,000 } \\ \\ =\frac { 60 }{ 4 } \\ \\ =15[/tex]
As 15% of 4,000 is 600, the percentage change was -85%.