int ledPin = 13;
int delayPeriod = 100;



void setup() {
  pinMode(13, OUTPUT);



  //------- SIMPLE ARITHMATIC------
  Serial.begin(9600);
  int degC = 20;
  int degF;
  int degf = degC * 9 / 5 + 32;
  Serial.println(degF);
  //OR
  degF = ((degC * 9) / 5) + 32;
  Serial.println(degF);


}

void loop() {

digitalWrite(ledPin, HIGH);
delay(delayPeriod);
digitalWrite(ledPin, LOW);
delay(delayPeriod);

delayPeriod = delayPeriod + 100;

if (delayPeriod > 3000)
{
  delayPeriod = 100;
}
}