Each writer for the local newspaper is paid as follows: a dollars for each of the first z stories each month, and a + b dollars for each story thereafter, where a > b. How many more dollars will a writer who submits z + a stories in a month earn than a writer who submits z+ b stories?  Choose the correct choice from the following choices.
A) (a – b)( a + b + z)
B) a – b
C) a^2 – b^2
D) z( a – b)
E) az + bz – az
total earned for z+a stories =a + a(a+b)   total earned for z+b stories =a+ b(a+b)   difference = a+a(a+b) -a -b(a+b)   =(a+b)(a-b) =a^2-b^2   answer is a^2 – b^2
<result>C</result>
Each writer for the local newspaper is paid as follows: a dollars for each of the first z stories each month, and a + b dollars for each story thereafter, where a > b. How many more dollars will a writer who submits z + a stories in a month earn than a writer who submits z+ b stories?