Task: Question Answering
Input (English): Problem: there are 4 people of different heights standing in order of increasing height . the difference is 2 inches between the first person and the second person , and also between the second person and the third person . the difference between the third person and the fourth person is 6 inches and the average height is 77 . how tall is the fourth person ? 
Options: a ) 79 , b ) 81 , c ) 83 , d ) 85 , e ) 87
Output (English): c