At the bottom of river there is a lamp. On what minimal distance from the subject its reflection will be placed at the bottom of the river? Refraction index of water is 1.5, depth of the river is 2.5 m.

Question

At the bottom of river there is a lamp. On what minimal distance from the subject its reflection will be placed at the bottom of the river?  Refraction index of water is 1.5, depth of the river is 2.5 m.