Task: Question Answering
Input (English): Problem: an empty fuel tank is filled with brand z gasoline. when the tank is 3 / 4 empty, it is filled with brand y gasoline. when the tank is half empty again, it is filled with brand z gasoline. when the tank is half empty again, it is filled with brand y gasoline. at this time, what percent of the gasoline in the tank is brand z ?
Options: a. 40 %, b. 41 %, c. 43.75 %, d. 42 %, e. 44 %
Output (English): c