3 n + 15 m-2 n + 20 n + 7 n

To simplify the expression \(3n + 15m - 2n + 20n + 7n\), combine like terms.

1. Combine the terms with \(n\): \[ 3n - 2n + 20n + 7n = (3 - 2 + 20 + 7)n = 28n \]

2. The term with \(m\) is just \(15m\).

So, the simplified expression is: \[ 28n + 15m \]