#define CAYENNE_PRINT Serial  
#include <CayenneEthernet.h>
#define VIRTUAL_PIN V0

char token[] = "token";

float sensorValue;

void setup() 
{
  Serial.begin(9600);
  Cayenne.begin(token);
}
void loop() 
{
  Cayenne.run();
  int analogValue = analogRead(A0); // read the input on analog pin 0
  float a = 5; //I am measuring 25V on sensor, 25V/5V=5
  float b = 0.00455522971; //Voltage on 5V pin on arduino / 1023, My voltage is 4.66V > 4.66/1023=0.00455522971
  sensorValue = analogValue * a * b;
  Serial.println(sensorValue);
  delay(500); //measuring every 0.5s
}

CAYENNE_OUT(VIRTUAL_PIN)
{
  Cayenne.virtualWrite(VIRTUAL_PIN, sensorValue);
}