According to the graph, what is the value of the constant in the equation below?

a. 8
b. 12
c. 6
d. 4

You answer is 12 because that is where on the graph it is the most constant

b.an increase in a causes b to decrease

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