Find Distance from Screen to Slits in Double Slit Experiment

[rocapp]

Homework Statement

See attached image

Homework Equations

y=L*tan(theta)
m*(lambda)=d*sin(theta)

The Attempt at a Solution

Lambda = 640 nm = 6.4x10^-4 mm

m*(lambda)=d*sin(theta)

1*(6.4x10^-4 mm) = (0.25 mm)*sin(theta)

theta = 0.15 degrees

y = L*tan(theta)

This is where I am not sure. I know I need to plug in y and theta. But I think my y value is wrong. How can I know for sure what the distance between the maxima are? The graph that is given seems to be too poor to tell.

 

[Doc Al]

This is where I am not sure. I know I need to plug in y and theta. But I think my y value is wrong. How can I know for sure what the distance between the maxima are? The graph that is given seems to be too poor to tell.

The diagram seems clear enough to me. Hint: The distance of 2.0 cm seems to be exactly between which two maxima? (Don't think you need to use m = 1.)