You and your friends want to tour the southwest by car. You will visit the nine states below, with the following rather odd rule: you must cross each border between
neighboring states exactly once (so, for example, you must cross the Colorado-Utah
border exactly once). Can you do it? If so, does it matter where you start your road trip?
What fact about graph theory solves this problem?

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?