The borehole is extended in a straight line and leaves the water-bearing rock layer at a depth of 3600 m below the Earth's surface. The exit point is described in the model as a point $R$ on the line $P Q$. Determine the coordinates of $R$ and calculate the thickness of the water-bearing rock layer rounded to the nearest metre. (for verification: $x _ { 1 }$ and $x _ { 2 }$ coordinate of $R : 1.04$ )