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 A(t) denote Nour's altitude relative to sea level A (measured in meters) as a function of time t (measured in hours).
Write the function's formula.