69. 18.3 ft

71. 42.4 m

73. 5.9 ft from the wall on the opposite sides, along the major access

75. ${\displaystyle \frac{x^2}{20,067.5556}}+{\displaystyle \frac{y^2}{19,894.1067}}=1$

77. ${\displaystyle \frac{x^2}{1,311.8884}}+{\displaystyle \frac{y^2}{1,253.2128}}=1$

79. Perihelion: 364,224.1427 km; aphelion: 404,581.8573 km

81. ${\displaystyle \frac{x^2}{16,785,409}}+{\displaystyle \frac{y^2}{16,784,680}}=1$