Question 665258
The difference in their ages will always be {{{ 66 - 18 = 48 }}} years
If Mike's age is {{{ m }}} and Grandmother's age is {{{ 9m }}}, 
then {{{ 9m - m = 48 }}}
{{{ 8m = 48 }}}
{{{ m = 6 }}}
Mike was 6 years old 12 years ago since {{{ 18 - 12 = 6 }}}