(3)[ On the day specified in the notice issued under sub-section (2) or as soon afterwards as may be, after hearing such evidence as the assessee may produce and such other evidence as the Assessing Officer may require on specified points, and after taking into account all relevant material which he has gathered, the Assessing Officer shall, by order in writing, assess the net wealth of the assessee and determine the sum payable by him on the basis of such assessment.