Hey

Minima

a sinθ = nλ ; n =1 and x/f = λ/a

Therefore, with given parameters x = 3.912 * 10^-5 m

Maxima

a sinθ = (2n+1)λ/2 ; n = 1 and sinθ = x/f

x =f3λ/2a

Therefore; x = 5.868 * 10^-5 m

Hence, distance between fringes;

x = x - x

5.868*10^-5 - 3.912 * 10^-5 m = 1.956 * 10^-5 m

For further doubts, ask us.