The triangles in question 15 are proportional, so they are similar. Meaning that their angles are the same, so <B=<E, or <B=30 degrees.
For #17, the formula for the area of a circle is a=pi*r^2. The radius, in this instance, is 1/2 of 27, or 13.5. Plug it into the formula: a=pi*13.5^2. a=pi*182.25. If you want to simplify it further, a=572.265.
#19, same formula as #17. a=pi*r^2. a=pi*6^2. a=pi*36. a=113.04 or 113m^2.
#20, Wow this is a complicated one. Anyway, the area of the square in the middle is obviously 9m. The area of all of the circles is a=pi*1.5^2 DIVIDED BY TWO, since they're half circles. a=pi*2.25/2, a=7.065/2. a=3.5325. Since there are 4 of them, multiply that number by 4... 14.13. Add 9 to that to get the area of the whole figure: 23.13m(^2). Hope this helps.
