In the ratio 2:3 going to 28:? there is a pattern. You multiply 2 by 14 to get to 28, so if you multiply 3 by 14 you get 42. Add 42 to 28 for the total amount of students in class!
After striking a pair of arcs from each endpoint of a line segment, just join the intersection point of the 1st pair (above the segment) with the intersection point of the 2nd pair (under the segment) And this is how you construct the segment's perpendicular bisector