Please help ASAP! Does this represent a nonlinear function, a linear function, or not a function?

Negative 5 1/12 + negative 4 1/4 + 6 3/4

Find the area of the regular hexagon if a side is 20 cm.

Two airplanes start at the same place and travel in opposite directions,one at 395 miles per hour and the other at 422 miles per hour. how many hours will it take for the planes to be 2451 miles apart?