Numerical on plinth area

Questions--Prepare a preliminary estimate of a polytechnic building for 800 students in order to assess the amount based on the following :

Carpet area required per student=1.20sq.m

Area of corridor, verandah and staircases etc = 20% of the plinth area

Area of walls = 15% of the plinth area

Consider plinth area rate = 3500rs per Sq. m

Cost of water supply = 5% of the building cost

Cost of sanitation = 7% of the building cost

Cost  of electrification = 12% of the building cost

Cost of approach road and boundary wall = 3% of the building cost

Contingencies and supervision charges = 5% and 2.5% respectively

Solution : in this question we have to find carpet are first then plinth area. See the image below :