Given parameters:
Elevation of Town M = 282ft
Elevation of Town R = 679ft
Unknown:
How much higher is Town R than M = ?
Solution:
Town M lies below the sea level whereas Town R is above the sea level.
Graphically:
Town R 679ft
↑
↑
↑
↑
↔↔↔ Sea level
↓
↓
Town M 282ft
Town R is 282ft + 679ft higher than Town M = 961ft