Answer
The distance between maxima is $~~5.0~mm$
Work Step by Step
In part (a), we found that the angular separation is $0.01~rad$
We can find the distance $x$ between the maxima:
$\frac{x}{50.0~cm} = tan~(0.01~rad)$
$x = (50.0~cm)~tan~(0.01~rad)$
$x = 0.50~cm$
$x = 5.0~mm$
The distance between maxima is $~~5.0~mm$.
