Photo above! find the area of this triangle (it says the answer is 405 but all i get when i do it is 810) !

it will cost dollar $540

the living room is 3 which means if we divide 325/3 then we get $108

therefore if 1part of the living room cost $108 and 3 costed $325

then total 5part of the room will cost 5*108 which gives $540

pls refer ro the top for answer