Answer:
80 cm
Step-by-step explanation:
To find the minimum distance from the slits to the screen you use the following formula for the m-th fringe of the interference pattern:

m: order of the fringe
λ: wavelength = 632.8*10^-9 m
D: distance to the screen
d: distance between slits = 0.034*10^-3
for the distance between fringes you have:
( 1 )
By replacing the values of the parameters in (1) you can find the distance D to the screen:

hence, the distance from the slits to the screen is 80 cm