A(m+n)+6(m+n)

To simplify the expression \( a(m+n) + 6(m+n) \), you can factor out the common term \( (m+n) \):

\[ a(m+n) + 6(m+n) = (m+n)(a + 6) \]

So the simplified expression is:

\[ (m+n)(a + 6) \]