Abat flies toward a wall, emitting a steady sound of frequency 1.70 khz. this bat hears its own sound plus the sound reflected by the wall.

I believe the question is missing this sentence: how fast should the bat fly in order to hear a beat frequency of 8.00 Hz? The solution would be like this for this specific problem:

8.00 / 1700 = 2 * v / 340m/s 
v = 0.8 m/s 

So, in order to hear a beat frequency of 8.00 Hz, the bat should fly 0.8m/s.

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.