Verified answer

a)2m^3-18m=2m(m^2-9)=2m(m-3)(m+3)

 b)7m^2+14mn+7n^2=7(m^2+2mn+n^2)=7(m+n)^2

c)6n^3+6m^3=6(m^3+n^3) =6(m+n)( m^2-mn+n^2)

d)16m^4-81n^4=(4m^2)^2-(9n^2)^2=(4m^2-9n^2)(4m^2+9n^2)