we can see that 
curve is a straight line 
y-axis is price(p)
x-axis is number of glasses (x)
so, firstly we will find slope 
we can select any two points 
(0,0) and (2,9)
x1=0, y1=0 , x2=2 , y2=9

now, we can plug values


now, we can use point slope form of equation 

so, we can plug it 


now, y is p 
so, we get our equation as
 ................Answer
................Answer