Question 680871
To arrive at some future age for them both, 
add {{{ x }}} to both their ages
{{{ 48 + x }}} = Grandmother's age {{{ x }}} years in the future
{{{ 8 + x }}} = Granddaughter's age {{{ x }}} years in the future
given:
{{{ 48 + x = 3*( 8 + x ) }}}
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{{{ 48 + x = 24 + 3x }}}
{{{ 2x = 24 }}}
{{{ x = 12 }}}
and
{{{ 48 + x = 48 + 12 }}}
{{{ 48 + x = 60 }}}
and
{{{ 8 + x = 8 + 12 }}}
{{{ 8 + x = 20 }}}
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When I am 60, I will be 3 times older than my granddaughter
who will be 20
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Notice that the difference in their ages in {{{ 40 }}}
as it is presently.