You can
put this solution on YOUR website! .
This passage "Adam was 4 times older than his sister" is prohibited (is strongly not recommended for use)
in Math problem formulations in English.
It should be replaced by
"Adam was 4 times as old as his sister's age",
or
"Adam was 3 times as old as his sister's age",
depending on which idea, precisely and exactly, you want to bring to a reader.