Answer
$2,500$
Work Step by Step
With $b=100$, complete the square by adding $\left(\frac{b}{2}\right)^2$:
$\left(\dfrac{b}{2}\right)^2=\left(\dfrac{100}{2}\right)^2=(50)^2=2500$
Therefore, to complete the square, add $2500$ to the given expression.