The fringe width, \(\beta\), is calculated as \(\beta = \frac{\lambda D}{d} = \frac{5 \times 10^{-7} \times 2}{3 \times 10^{-4}} = 10 \times 10^{-3} \, \text{m}\).
For the 3rd maxima:
The position of the 3rd maxima, \(y_3\), is \(y_3 = 3\beta = 10 \times 10^{-3} \, \text{m} = 10 \, \text{mm}\).