Answer:
[tex]-21 - 7C[/tex]
Step-by-step explanation:
To simplyfy this expression you should begin to pair like terms. Like terms in this context means terms that are constant are different from those with variable C (multiples of C) which are also different from terms with variable D (multiples of D. Below I will pair like terms within parentesis.
[tex]5C- 3-D -12 C+D -6 = (-3-12 -6) + (5C-12C) + (-D+D)[/tex]
Note how the D-terms will cancel out from this expression. Now we can just sum up the terms within each parenthesis.
[tex](-3-12 -6) + (5C-12C) + (-D+D) = -21 -7C + 0 = -21 - 7C[/tex]
