Assuming that everything remains constant, after one million years, Mount Marshak would be 5.1km tall. This is because the mountain would be uplifted by 1.3km after a million years but also eroded 1.5km after a million years. The difference is 0.2km in the direction of erosion. This means the mountain would be 0.2km smaller than it was before. 5.3-0.2=5.1.