Brianne is three times as old as camila. four years from now she will be two-times as old as camila. how old are brianne and camila now?

B=brianne present age
c=camila present age

b=3c    (brianne is three times as old as camila)

b+4=2(c+4)     (four years from now she will be two times as old as Camila)

b + 4 = 2c + 8
b = 2c + 8 - 4
b = 2c + 4
Replace b with 3c
3c = 2c + 4
3c - 2c = 4
c = 4 

Camila is four years old. 

b+4=2c+8
b=2(4)+4
b=8+4
b=12
Brianne is 12 years old.