Which relation is a function?

In the equations, a and b represent the price per night for a room in hotel a and hotel b, respectively, w weeks after september 1 last autumn. what was the price per night in hotel a when it was equal to the price per night in hotel b? a = 240 − 20w b = 320 − 30w

The parabola x = y² - 9 opens: a.)up b.)down c.) right d.)left

Consider the proof. given: segment ab is parallel to line de. prove: what is the missing statement in step 5?