Steps :
Consider the lamp as a point and table as a plane.
Let ABCD be the top view of table and E be the position of lamp.
Let AD be y-axis and CD be x-axis.
From point E draw EF ⊥ AD and EG ⊥ CD.
Measure EF = 25 units (let) and EG = 30 units (let).

The distance of the point from the x-axis and y-axis is x and y respectively, so the coordinates of table lamp will be (x, y).
E(x, y) = (EF, EG) = (25, 30).
Hence, position of lamp on table can be described by coordinates (25, 30).