The class has 28 student. One group has four more students so surat 4 from 28. 28-4=24 since one of the groups have twice as many students as the other divide 24 by 3. 24 / 3 = 8. It says 1 group has for more than twice the other group so that would mean 2/3 of 24 and 4 would be the answer 16+4=20. The first group had 8 students, the other group has 20 students.
First divide bot sides of the formula by 1/2(3.14):-
2A / 3.14 = r^2
r = sqrt (2A/3.14)
Letter C. Is correct I think, hope this helped.