Geometry problems 8 (70..79) problems 60..69 problems 80..89 70. Calculate radius R. 71. Calculate the colored area. 72. Calculate radius r. 73. Calculate the colored area. 74. Calculate radius R. 75. Calculate radius R of the quarter circle. 76. Calculate the ratio r/R. 77. Calculate the colored area. 78. Calculate the radius R/r.(Golden ratio). 79. Calculate the colored area.