Respuesta :

frika

Answer:

[tex]3(1+7a+5b)[/tex]

Step-by-step explanation:

The distributive law states that

[tex]a\cdot (b+c)=a\cdot b+a\cdot c.[/tex]

The expression 3+21a+15b consists of three terms:

  1. 3=3·1;
  2. 21a=3·7a;
  3. 15b=3·5b.

You can see that 3 is the common factor of these three terms, thus

[tex]3+21a+15b=3(1+7a+5b).[/tex]