Answer
$D = 0.88~mm$
Work Step by Step
It is given in the question that $D = w$
We can find the diameter of the aperture:
$w = \frac{2.44~\lambda~L}{D}$
$D^2 = 2.44~\lambda~L$
$D = \sqrt{2.44~\lambda~L}$
$D = \sqrt{(2.44)(633\times 10^{-9}~m)(0.50~m)}$
$D = 8.8\times 10^{-4}~m$
$D = 0.88~mm$