12 5 + n Cross multiply the fractions
--- = ----------
8 n - 3
12(n - 3) = 8(5 + n) divide by 4 on both sides of the equal sign
3(n - 3) = 2(5 + n) distribute on each side
3n - 9 = 10 + 2n subtract 2n from both sides ...
3n - 2n -9 = 10
n = 10 + 9 add 9 to both sides ...
n = 19