Can anyone explain #4 on how to do it

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

x=-7

step-by-step explanation:

x+3=-10

-10+3=-7

x=-7