Which is the formula used to calculate flow-through? 

a. (GOP This period – GOP Last period) / (Total Revenue This Period – Total Revenue Last Period)

b. (GOP This period + GOP Last period) / (Total Revenue This Period – Total Revenue Last Period)

c. (GOP This period – GOP Last period) / (Total Revenue This Period + Total Revenue Last Period)

d. (GOP This period + GOP Last period) / (Total Revenue This Period + Total Revenue Last Period)