Contour farming is a method for plowing across the slope of steep hills

I believe that contour farming, if on mountainsides, is like the Incas did ie building horizontal terraces to retain the soil and allows the farmers to utilize even relatively steep mountains in the Andes for agriculture thus not wasting valuable land for cultivation.

980 is the correct answer

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.