if x and y are integers such that ( x + 1 ) ^ 2 is less than or equal to 81 and ( y - 1 ) ^ 2 is less than 64 , what is the sum of the maximum possible value of xy and the minimum possible value of xy ?
"( x + 1 ) ^ 2 < = 81 x < = 8 x > = - 10 ( y - 1 ) ^ 2 < 64 y < 9 y > - 7 max possible value of xy is - 10 × - 6 = 60 minimum possible value of xy is - 10 × 8 = - 80 - 80 + 60 = - 20 answer : b"
add(sqrt(81), sqrt(64))