Which expression represents the phrase “one third the sum of 12 and a number”?

Math each whole number with a rational,exponential expression

Acertain volume of water contains 100000 hydrogen atoms and 50,000 oxygen atoms how many hydrogen atoms are in a volume of water containing 4 million oxygen atoms

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?