The expression is 14a - 72r - c - 34d. Let's rewrite it: 14a + (-72r) + (-c) + (-34d)
The coefficient of a term is the value beside the term. For example, the coefficient of 5x term is 5. For the a-term (14a) of our expression, the coefficient is 14. The coefficient of the c-term (-c) will, therefore, be -1: -c = -1c