15 - 1/6n = 1/6n - 1
rewrite
1/6n - 1 = 15 - 1/6n
add 1/6 n to both sides
1/6n - 1 + 1/6n = 15 - 1/6n + 1/6n
Simplify
2/6n - 1 = 15
1/3n - 1 = 15
add 1 to both sides
1/3n - 1 + 1 = 15 +1
1/3n = 16
Multiply 3 to both sides
1/3n * 3 = 16 *3
3/3n = 48
n = 48