1hmm trying...
at t=0, position of P(object) = x,y,z (say)
position of image = I = -x,y,z
at t=1 sec,
position of P = x+3, y+4, z+5
its image = I = -(x+3), y+4, z+5
change in position of image in 1 sec = -3,4,5
change in position wrt mirror = -3i+4j+5k - (5j) = -3,-1,5
ther4, vel wrt mirror : -3i -1j +5k cm/s
vel wrt to object : ( -3i+4j+5k) - (3i+4j+5k) = -6i cm/s
