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

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

1. First, let's group the \( n \) terms: \[ 3n - 2n + 7n = (3 - 2 + 7)n = 8n \]

2. Now let's group the \( m \) terms: \[ 15m + 20m = (15 + 20)m = 35m \]

Putting it all together, we have: \[ 8n + 35m \]

So, the simplified expression is: \[ 8n + 35m \]