The teacher selerated her class of twenty eight students into two groups. one group has four more than twice as many students as the other group how many students are in each group

First, let one of the groups equal "x students". The other group must then be       "(2x+4) students" because it says in the problem that one group has 4 more than twice as much as the other group. the equation you can use to figure out what "x" equals is x+(2x+4)=28 because there are 28 students in total. By finding "x" which is equivalent to group 1, you can also find group 2 by plugging the number you got for x into the expression "2x+4".
x+2x+4=28  3x=24                                              2(8)+4=group 2
3x+4=28      x=8 (group 1 = 8 students)             20=group 2
3x+4=28

You want to isolate your variable.