An arrow is fired directly horizontal off a cliff that is 10.0 meters tall with a velocity of 65.5m/s how long is the arrow in the air?

Ascientist notices that an oil slick floating on water when viewed from above has many different colors reflecting off the surface, making it look rainbow-like (an effect known as iridescence). she aims a spectrometer at a particular spot and measures the wavelength to be 750 nm (in air). the index of refraction of water is 1.3