Question

If the angle θ in the two-source interference equations is small, then using small-angle approximations yields the equation ym=r(m+1/2)λd, where r is the distance from the sources to the points where they are being detected (in young's experiment the screen, in this example the road), and ym is the distance from the central maximum to the minimum of order m. use this equation to find the distance from the central maximum to the minimum in the previous part

Answer 1

This problem is missing some details because it doesn’t tell you what to use for “R”. But let us use the distance to the road (5000 m):
ym = R * (m + 1/2) λ / d
ym = 5000 * (0 + 1/2) * 300 / 400
ym = 1875
1900 m is the answer for the question which is the distance.