A correlation coefficient of 1 or -1 indicates that the variables form a perfect linear relationship.
If you multiply $60 by 0.15 you'll get 9 which is the taxes of the meal. Since he leaves the same percentage of tip, now we add 9+9 and get $18..
60+18=78
Triangles are the easiest shape to make a hexagon out of. You can do this by lining up 6 triangles where each base of the triangle lines up.
√18 ÷ √12 = 1.22474487139159