Help? An atom of hydrogen has a mass of about 1.66 x 10^-25 grams. An atom of oxygen has a mass of about 2.656 x 10^-23 grams. How many times the mass of the hydrogen atom is the mass of the oxygen atom? Give your answer in scientific notation.

The variable z is directly proportional to x, and inversely proportional to y. when x is 4 and y is 13, z has the value 1.2307692307692. what is the value of z when x= 9, and y= 20

The number of revolutions of two pulleys is inversely proportional to their diameters. if a 24-inch diameter pulley making 400 revolutions per minute is belted to an 8-inch diameter pulley, find the number of revolutions per minute of the smaller pulley.

The variable in a relation who’s value depends on the value of the independent variable is called what?