What is the reason for step 7 in the proof above?

answer: the anser is 3

step-by-step explanation:

c- 2o is equal to 9

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