\(\frac{n}{2}-\frac{3n}{4}+\frac{5n}{6}=21\)
L.C.M. of the denominators, \(2, 4\), and \(6\), is \(12\).
Multiplying both sides by \(12\), we obtain
\(6n - 9n + 10n = 252\)
\(\Rightarrow\) \(7n = 252\)
\(\Rightarrow\) \(n = \frac{252}{7}\)
\(\Rightarrow\) \(n = 36\)