the average ( arithmetic mean ) of 7 , 8 , 10 and 11 equals the average of 2 , 9 , 13 , and
"7 + 8 + 10 + 11 = 2 + 9 + 13 + x 36 = 24 + x or , x = 12 hence , answer will be ( d ) 12"
subtract(add(add(7, 8), 10), add(add(multiply(11, const_3), 2), 9))