if a ( a - 4 ) = 21 and b ( b - 4 ) = 21 , where a ≠ b , then a + b =
"a ( a - 4 ) = 21 and b ( b - 4 ) = 21 = > a , b must be integers and if a is - 3 or 7 , b will be 7 and - 3 respectively = > a + b = 4 ans : c"
subtract(subtract(subtract(subtract(add(add(4, 21), subtract(4, 21)), const_1), const_1), const_1), const_1)