int buttonA = 2;
int buttonB = 3;

void setup(){
  Serial.begin(9600);
  pinMode(buttonA, INPUT_PULLUP);
  pinMode(buttonB, INPUT_PULLUP);
  pinMode(10, OUTPUT); //Sum, Red LED
  pinMode(12, OUTPUT); //Carryout, Yellow LED
}

void loop() {
  int inputA = digitalRead(buttonA); // read voltage on pin
  int inputB = digitalRead(buttonB);

  if(inputA && inputB) { 
    digitalWrite(10, LOW);
    digitalWrite(12, HIGH);
  } else if (inputA || inputB) {
    digitalWrite(10, HIGH);
    digitalWrite(12, LOW);

  } else {
    digitalWrite(10, LOW);
    digitalWrite(12, LOW);
  }
}