Please answer and explain nummber 7 i will give brainlest

What are linear equations? could'ya explain too me, ? ! and how do you see what graph is a proportional relationship?

An incoming airplane is x miles due north from the control tower at an airport. a second incoming airplane is y miles due east of the same control tower. the shortest distance between the two airplanes is z miles. which of the following functions would best model the situation above?

How to do a maths question? i have a mock