Mary is x years old.
Consuela is three times as old as Mary, so she's 3x years old.
In 10 years Mary will be x+10 years old, and Consuela will be 3x+10 years old.
In 10 years Consuela will be twice Mary's age, so she'll be 2(x+10) years old.
[tex]3x+10=2(x+10) \\
3x+10=2x+20 \\
3x-2x=20-10 \\
x=10 \Leftarrow \hbox{Mary's age} \\ \\
\hbox{Consuela's age:} \\ 3x=3 \times 10=30[/tex]
Now Consuela is 30 years old.
[tex]30-4=26[/tex]
4 years ago Consuela was 26 years old.
