What is a parabola and how does it differ from a linear graph

A parabola graph is a graph where the line is curved. A linear graph is a graph where the line is straight. 

A parabola is curved. A linear graph is a straight line.

A parabola is of degree order 2. A linear graph is of degree order 1.

A parabola has varying slope along the curve. A linear graph has constant slope throughout the line.

$18

Step-by-step explanation:

we proceed by first solving for the unit cost of a sheet

then calculate the cost for any number of sheet

We are told that a builder could buy 6 sheets for the cost of $9

this means that one sheet would cost 9/6= $1.5

Now the builder buys 12 sheets

therefore the cost of 12 sheets will be

12*1.5= $18