Given that,

$40\% of 5051-\frac{3}{7}\text{th} of 999=?$

It can be written as 

50% of 5000-$\frac{3}{7}\text{th}$ of 987=?

⇒ $\frac{1}{2}$×5000-3×141=?

⇒ 2500-423

⇒ 2077≈2045

Hence, Option B is correct.