if the average ( arithmetic mean ) of a and b is 20 , and c – a = 30 , what is the average of b and c ?
"a + b / 2 = 20 = > a + b = 40 a = c - 30 . . . sub this value c - 30 + b = 40 = > c + b = 70 = > c + b / 2 = 35 answer : d"
subtract(multiply(30, const_2), multiply(20, const_2))