Question

What is the answer to 7a + 21b + 42c?

Answer 1

So, lets forget about the letters for now okay? So 7+21=28
28+ 42 = 70
Since we don't know what the letters are, we can't use them in the equation, so we then answer this question with 70abc
Hope that was helpful and explanitory! :)

Answer 2

7 goes into the three numbers so...

7(a + 3b + 6c)

Is that what you're asking for?