Carlos is 8 years older than Maria. 4 years ago maria was two thirds as old as Carols. How old are they?
I call the age of Carlos today
The first relationship is
the second relationship is that
I substitute the first in the second
multiplying by 3 both sides
Just to verify, Carlos is 8 years older of Maria (he is 36 and Maria is 28) and four years ago Maria was 24 that is two third of the age of Carlos.