ANSWER
[tex]14(10c - a + 2)[/tex]
EXPLANATION
The given expression is
[tex]140c+28-14a[/tex]
We can rewrite this as:
[tex]140c - 14a + 28[/tex]
The greatest common factor is 14.
We factor 14 to obtain:
[tex]14(10c - a + 2)[/tex]
This is completely factored.