Dear Student,
Solution) Gaurav's age = x years and Saurav's age = y years
Therefore,  ATQ,
$\frac{x}{y}=\frac{5}{7}\phantom{\rule{0ex}{0ex}}7x=5y\phantom{\rule{0ex}{0ex}}7x-5y=0$
Now, after 3 years,
$\frac{x+3}{y+3}=\frac{4}{5}$
5x + 15 = 4y + 12
5x - 4y = 12 - 15
5x - 4y = - 3
So, the option B is correct.
Regards!

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