To simplify the expression 6c + 4d - c - 7d, we can first combine the like terms, which are the terms that have the same variable and the same exponent:
6c - c + 4d - 7d
Simplifying this expression further by combining the like terms, we get:
5c - 3d
Therefore, 6c + 4d - c - 7d simplifies to 5c - 3d.