Question 964374
Let F denote the father's age. Let B denote Adam's brother's age. Then
{{{F=x+21}}}
{{{B=x+3}}}
{{{x+B=F}}}
So we conclude
{{{x+(x+3)=x+21}}}
{{{2x+3=x+21}}}
{{{x=18}}}
Adam is 18 years old.
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