tentukan nilai masing masing

siswa 1 = x1 = x2 - 2
siswa 2 = x2
siswa 3 = x3 = x1 + 4 = (x2 - 2) + 4 = x2 + 2

x1 + x2 + x3 = 21
x2 - 2 + x2 + x2 + 2 = 21
3x2 = 21
x2 = 7
x1= x2 - 2 = 7 - 2 = 5
x3 = x1 + 4 = 5 + 4 = 9

#maaf jika salah semoga membantu

jumlah nilai 3 siswa = 21

anggap siswa 1 a, siswa 2 b, siswa 3 c

a=b-2
c=a+4

jadi, c=a+4
         =(b-2)+4
         =b+2

a+b+c = 21
(b-2) + b + (b+2) = 21
3b=21
b=7

a= b-2
  =7-2
  =5

c= a+4
  =5+4
  =9

jadi, a=5, b=7, c=9