Nour drove from the Dead Sea up to Amman, and her altitude increased at a constant rate. When she began driving, her altitude was 400 meters below sea level. When she arrived in Amman 2 hours later, her altitude was 1000 meters above sea level. Let y represent Nour's altitude (in meters) relative to sea level after xxx hours.
Complete the equation for the relationship between the altitude and number of hours.