You arrive in my class 50 seconds after leaving math which is 90 meters away. How fast did you travel?

What human activity increases beach erosion?

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium

Ahelium balloon contains 16.9 l of helium at stp. how many atoms of helium are in the balloon