If you know the wavelength of any form of electromagnetic radiation, you can determine its frequency because?

If anyonee has done the momentum lab practical in physics can you give me the answers i am s lostt rnn : (

Only 3% of the water on earth is usable by humans. even though that 3% is through the water cycle, we still need to be careful not to waste water.

The radioactive isotope of lead, pb-209, decays at a rate proportional to the amount present at time t and has a half-life of 3.3 hours. if 1 gram of this isotope is present initially, how long will it take for 80% of the lead to decay? (round your answer to two decimal places.)