Let us consider the lamp as a point A and table as a plane.
Take any two perpendicular edges of the table. Measure the distance of the lamp from the longer edge AD (denoting y-axis), let it be 25 cm.
Again, measure the distance of the lamp from the shorter edge AB (denoting x-axis);
let it be 15 cm. Therefore, the position of the lamp can be written as (15, 25).