Slope of the topographic surface

Téma:
Přímky
Star Villa (1555) is surrounded by game reserve "Obora Hvězda". Determine the highest slope of the circled area.
Slope is determined by contour lines. The closer countours means the steeper terrain. The smallest distance of neigbouring contour lines is estimate by the circle with radius r. slope = rise (5) over run (2r).