4. The water in Earth's atmosphere blocks most of the infrared waves coming from space. In order to observe light of this wavelength, the Kuiper Airborne Observatory has been developed. The observatory consists of an optical telescope mounted inside a modified C-141 aircraft. The plane flies at altitudes where the relative humidity is very low and where the incoming infrared radiation has not yet been significantly absorbed. Suppose a double-slit arrangement with a 15.0 m slit separation is used to analyze infrared waves received by the telescope and that a second-order maximum is observed at 19.5. Determine the wave's wavelength.