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2 answers:
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Let 
Ben's age
Let
Daniel's age
We know:
and
Plug the value of
into the second equation:
Since Ben is 20 years older than Daniel, Ben is 13+20=33 years old.
Let
We know:
and
Plug the value of
Since Ben is 20 years older than Daniel, Ben is 13+20=33 years old.