Question 1024331
Call her and her sister's age NOW, x and y.  Then we write
x = y + 4
Two years ago
x - 2 = 3(y - 2)
Now substitute the first equation into the second equation...we get
y+4 - 2 = 3(y - 2)
y + 2 = 3y - 6
8 = 2y and
y = 4
so that 
x = 8