let 'x' be the age of the boy at present
'y' be the age of his brother at present
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the boy is 10 years older than his brother
x = 10 + y ----------equation 1
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in 4 years, he will be twice as his brother's age
in 4 years, 'x+4' is the boy's age
'y+4' is his brother's age
x + 4 = 2(y+4) -------equation 2
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substitute equation 1 to equation 2
10 + y + 4 = 2(y+4)
10 + y + 4 = 2y + 8
10+4-8 = 2y-y
6 = y
y = 6
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Substitute y = 6 to equation 1
x = 10 + y
x = 10 + 6
x = 16
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Therefore the age of the boy is 16 and his brother's age is 6
