To add the binomials with the trinomials first arrange the similar terms.
For example take a binomial as (a+b) and a trinominal as (2a+3b+4c). To add both first arrange the similar terms as shown below,
[tex](a+b)+(2a+3b+4c)=(a+2a)+(b+3b)+(4c)[/tex]Now add the coefficient of the similar terms to get the desired result,
[tex](a+2a)+(b+3b)+4c=3a+4b+4c[/tex]